Amicus Curiae Brief — William Trevor Case, Petitioner v. Montana

No. 24-624

In the Supreme Court of the United States

__________

WILLIAM TREVOR CASE,

Petitioner,

v.

STATE OF MONTANA,

Respondent.

__________

On Writ of Certiorari to the

Supreme Court of Montana

__________

BRIEF OF THE CATO INSTITUTE AND

AMERICANS FOR PROSPERITY

FOUNDATION AS AMICI CURIAE IN SUPPORT

OF PETITIONER

__________

Lee A. Steven

Americans for Prosperity

Foundation

4201 Wilson Blvd., Ste. 1000

Arlington, VA 22203

(571) 329-1716

lsteven@afphq.org

August 6, 2025

Matthew P. Cavedon

Counsel of Record

Brent Skorup

Christine Marsden

CATO INSTITUTE

1000 Mass. Ave., N.W.

Washington, DC 20001

(706) 309-2859

mcavedon@cato.org

i

QUESTION PRESENTED

Whether law enforcement may enter a home without a search warrant based on less than probable

cause that an emergency is occurring, or whether the

emergency-aid exception requires probable cause.

ii

TABLE OF CONTENTS

QUESTION PRESENTED ........................................... i

TABLE OF AUTHORITIES ....................................... iii

INTEREST OF AMICI CURIAE ................................. 1

INTRODUCTION AND

SUMMARY OF ARGUMENT ................................... 3

ARGUMENT ................................................................ 5

I.

THE FRAMERS DID NOT

RECOGNIZE AN EMERGENCY AID

EXCEPTION TO THE FOURTH

AMENDMENT’S PROBABLE CAUSE

REQUIREMENT. ............................................ 5

II. A PROBABLE CAUSE

REQUIREMENT FOR HOME

ENTRIES PRESERVES THE

SANCTITY OF THE HOME. .......................... 7

III. A PROBABLE CAUSE

REQUIREMENT PROTECTS BOTH

HOMEOWNERS AND POLICE. .................... 9

CONCLUSION .......................................................... 11

iii

TABLE OF AUTHORITIES

Page(s)

Cases

Arizona v. Johnson, 555 U.S. 323 (2009) .................... 7

Boyd v. United States, 116 U.S. 616 (1886) ............ 6, 8

Carpenter v. United States, 585 U.S. 296

(2018) ........................................................................ 6

Ibrahim v. DHS, 62 F. Supp. 3d 909

(N.D. Cal. 2014) ....................................................... 7

Ker v. California, 374 U.S. 23 (1963) ........................ 11

McDonald v. United States, 335 U.S. 451

(1948) .................................................................. 9, 10

Payton v. New York, 445 U.S. 573 (1980) ................... 8

Semayne’s Case, 77 Eng. Rep. 194 (K.B. 1603)........... 9

Terry v. Ohio, 392 U.S. 1 (1968) .............................. 5, 7

United States v. Di Re, 332 U.S. 581 (1948) ............... 6

United States v. Reed, 572 F.2d 412

(2d Cir. 1978) ............................................................ 8

United States v. Vasquez-Algarin, 821 F.3d

467 (3d Cir. 2016) ..................................................... 9

United States v. Vega-Barvo, 729 F.2d 1341

(11th Cir. 1984) ........................................................ 7

Wilson v. Arkansas, 514 U.S. 927 (1995) .................... 9

iv

Other Authorities

Anthony Galaviz, Armed Homeowner Was

Victim Shot by Reedley Police Officer

During Burglary Suspect Hunt, FRESNO

BEE (Sept. 15, 2021) ............................................... 10

Devon W. Carbado, Stop-and-Strip Violence:

The Doctrinal Migrations of Reasonable

Suspicion, 55 HARV. C.R.-C.L. L Rev. 467

(2020) .................................................................... 7, 8

EDWARD COKE, THE FOURTH PART OF THE

INSTITUTES OF THE LAWS OF ENGLAND:

CONCERNING THE JURISDICTION OF COURTS

(1644) ........................................................................ 6

Emma Colton, Bodycam Footage Shows Police

Fatally Shoot Armed Homeowner After

Responding to Wrong House,

FOX 32 CHICAGO (Apr. 17, 2023) ........................... 10

Laura K. Donohue, The Original Fourth

Amendment, 83 U. CHI. L. REV. 1181 (2016)

...................................................................... 3, 6, 7, 8

MATTHEW HALE, PLEAS OF THE CROWN: OR,

A METHODICAL SUMMARY OF THE PRINCIPAL

MATTERS RELATING TO THAT SUBJECT (1682) .......... 6

Michael Gentithes, Exigencies, Not

Exceptions: How to Return Warrant

Exceptions to Their Roots, 25 U. PA. J.

CONST. L. 59 (2023) .................................................. 3

Peggy Lowe, Former KCPD Detective Violated

Cameron Lamb’s Rights, Federal Court

Rules in Wrongful Death Suit, KCUR

(Sept. 18, 2024) ....................................................... 10

v

Constitutional Provisions

U.S. CONST. amend. IV ............................................ 5, 8

1

INTEREST OF AMICI CURIAE1

The Cato Institute is a nonpartisan public policy

research foundation founded in 1977 and dedicated to

advancing the principles of individual liberty, free

markets, and limited government. The Cato Institute’s

Project on Criminal Justice was founded in 1999 and

focuses on the proper role of the criminal sanction in a

free society, the scope of substantive criminal liability,

the proper and effective role of police in their communities, the protection of constitutional and statutory

safeguards for criminal suspects and defendants, citizen participation in the criminal justice system, and

accountability for law enforcement officers.

Amicus curiae Americans for Prosperity (AFPF) is

a 501(c)(3) nonprofit organization committed to educating and training Americans to be courageous advocates for the ideas, principles, and policies of a free and

open society. Those key ideas include the freedoms and

rights protected by the Fourth Amendment to the

United States Constitution, including in particular the

freedom from unreasonable searches and seizures as

understood by the original framers of the amendment.

AFPF believes all Americans should be shielded from

the arbitrary exercise of the police power and that the

probable cause standard is key to that protection.2 As

part of its mission, AFPF appears as amicus curiae before federal and state courts.

1 Rule 37 statement: No part of this brief was authored by any

party’s counsel, and no person or entity other than amici funded

its preparation or submission.

2 Amicus AFPF takes no position in this brief on the constitu-

tionality of the exclusionary rule as the proper remedy for violations of the Fourth Amendment.

2

This case interests Cato and AFPF because it concerns the ability of police officers to unconstitutionally

enter a home without a warrant, unnecessarily endangering both police and civilians.

3

INTRODUCTION AND

SUMMARY OF ARGUMENT

The Fourth Amendment’s warrant requirement

was once relatively simple to understand and apply. If

an officer wanted to conduct a search, seize papers, or

enter a home, he had to get a warrant. See Laura K.

Donohue, The Original Fourth Amendment, 83 U. CHI.

L. REV. 1181, 1192 (2016).3 There were few exceptions,

and even these were construed narrowly, for the protection of officers, civilians, suspects, and the public.

Now, however, there is a “labyrinth of exceptions”

to the warrant requirement, each with their own nuances, caveats, and conditions. See Michael Gentithes,

Exigencies, Not Exceptions: How to Return Warrant

Exceptions to Their Roots, 25 U. PA. J. CONST. L. 59, 60

(2023).4 No underlying legal theory ties these exceptions together—except, perhaps, a desire to ease the

difficult job of policing. See id. at 63 (noting that many

exceptions arose from “narrow concerns over officers’

ability to respond to emergencies”).

The “emergency aid” exception is one such carveout: police officers may enter a home without a warrant if a person inside is experiencing, or is imminently threatened by, an emergency which requires

the officer to provide immediate assistance.

In this case, Montana police entered the home of

William Trevor Case without a warrant. The state argues that the resulting criminal evidence is admissible

because the officers were providing emergency aid.

The incident began in September 2021, when Case’s

ex-girlfriend called police and reported that Case had

3 Available at https://tinyurl.com/mvpmm629.

4 Available at https://tinyurl.com/6a7bc39u.

4

threatened suicide during a phone argument that

evening. Cert. Pet. at 6. Four officers went to Case’s

home, announced their presence, and observed

through a window an empty handgun holster and a

notepad—but no sign of life. Id. at 6–8. The officers

hesitated to enter, knowing that Case had a history of

mental health issues and that he had previously attempted “suicide by cop.” Id. at 2–3.

After about 40 minutes of discussion and preparation, the officers entered through the unlocked front

door. They conducted a sweep and found Case, alive

and hiding in a closet, which he revealed by opening a

curtain while an officer was sweeping the room. Id. at

7, 10. One officer, seeing a “dark object” near Case’s

waist, fired a shot that struck him in the arm and abdomen. Id. at 4, 10. The officers recovered a handgun

from a nearby laundry basket, and Case was taken to

a hospital. Id. at 10.

Case was later charged with felony assault of a police officer. Id. He moved to suppress the evidence obtained from the warrantless entry. Id. The trial court

denied the motion. Id. at 11. In a divided opinion, the

Montana Supreme Court upheld that decision under

the state’s “community caretaker” exception, which is

informed by the Ninth Circuit’s exigent circumstances

test. Id. at 12. Case now appeals and argues the evidence should be excluded because the officers lacked

probable cause to enter. Id. at 14.

Warrantless home entries based on mere reasonable suspicion of exigent circumstances violate the

Fourth Amendment and needlessly threaten the safety

of citizens and law enforcement. If Montana police did

5

not have probable cause to enter Case’s home, their

search should be declared unconstitutional.

If the Court declines to affirm a categorical warrant

requirement, it should at a minimum clarify that the

emergency aid exception requires probable cause. This

higher standard follows from the text of the Fourth

Amendment, preserves the sanctity of the home, and

reduces the risks warrantless entries pose to both residents and law enforcement.

ARGUMENT

I.

THE FRAMERS DID NOT RECOGNIZE AN

EMERGENCY AID EXCEPTION TO THE

FOURTH

AMENDMENT’S

PROBABLE

CAUSE REQUIREMENT.

Modern courts have outlined many exceptions to

the Fourth Amendment’s warrant and probable cause

requirements. In many jurisdictions, including Montana, the emergency aid exception allows officers to enter private dwellings without a warrant, based only on

reasonable suspicion that an emergency is occurring

inside. See id. at 12. Though this ahistorical, vague,

relaxed standard derives from Terry v. Ohio, 392 U.S.

1, 21–27 (1968), this Court has never applied Terry’s

reasonable suspicion standard to warrantless home

entries. See Cert. Pet. at 13–14.

Probable cause is the only standard that faithfully

preserves the protection the Framers intended against

unreasonable home entries. The Fourth Amendment

enshrines “[t]he right of the people to be secure in their

. . . houses . . . against unreasonable searches.” U.S.

CONST. amend. IV. Further, “no Warrants shall issue,

but upon probable cause.” Id. The Framers ratified the

Amendment to prevent the government from issuing

6

general warrants and adopting other intrusive practices characteristic of the British government. See

Donohue, supra, at 1323–24. The Fourth Amendment

provides essential protections against government intrusion into the lives of ordinary citizens, “secur[ing]

‘the privacies of life’ against ‘arbitrary power’ . . . ‘[and

placing] obstacles in the way of a too permeating police

surveillance.’” Carpenter v. United States, 585 U.S.

296, 305 (2018) (first quoting Boyd v. United States,

116 U.S. 616, 630 (1886); then quoting United States

v. Di Re, 332 U.S. 581, 595 (1948)).

Notably, at the Founding, the Fourth Amendment’s

ban on warrantless searches was understood as nearly

absolute. Police could not enter a “home, warehouse,

or place of business against the owner’s wishes to

search for or to seize persons, papers, and effects, absent a specific warrant.” Donohue, supra, at 1185. The

only common law exception to this requirement was

when a constable pursued a known felon into a home.

Id. at 1228–29 (citing MATTHEW HALE, PLEAS OF THE

CROWN: OR, A METHODICAL SUMMARY OF THE PRINCIPAL MATTERS RELATING TO THAT SUBJECT 91 (1682)).5

Departing from early Fourth Amendment jurisprudence, modern courts and scholars too often treat “reasonableness” as an independent standard, untethered

from the warrant and probable cause requirements,

and tethered instead to a vague sense of situational

5 And even on this point, there was not a consensus in the seven-

teenth and eighteenth centuries. Donohue, supra, at 1228 (“For

Coke, only a King’s indictment could justify breaking down doors

to effect arrest based on suspicion. A warrant issued by a justice

of the peace was insufficient.”) (citing EDWARD COKE, THE

FOURTH PART OF THE INSTITUTES OF THE LAWS OF ENGLAND: CONCERNING THE JURISDICTION OF COURTS 177 (1644)).

7

“reasonableness.” See Donohue, supra, at 1191–93.

This flawed, newer understanding does not reflect the

intent of the Framers and has allowed courts to

weaken Americans’ Fourth Amendment protections.

See id. at 1240–1305. Far from supporting a “reasonable suspicion” standard for warrantless entry, the original reasonableness standard requires that “outside of

apprehending a known felon, a warrant [is] required.”

Id. at 1192. Constitutional unreasonableness, therefore, is not the absence of reason, but the absence of a

warrant. Id. (“What ‘unreasonable’ meant in the seventeenth century was ‘against reason,’ which translated into ‘against the reason of the common law.’”).

Reasonable suspicion is an atextual standard that

has been used to justify myriad “muscular investigatory practice[s].” Devon W. Carbado, Stop-and-Strip

Violence: The Doctrinal Migrations of Reasonable Suspicion, 55 HARV. C.R.-C.L. L Rev. 467, 490 (2020);6 see

also Terry, 392 U.S. at 1 (stop-and-frisk searches); Arizona v. Johnson, 555 U.S. 323 (2009) (frisks of vehicle

passengers); United States v. Vega-Barvo, 729 F.2d

1341 (11th Cir. 1984) (stop-and-strip and X-ray

searches at the border); Ibrahim v. DHS, 62 F. Supp.

3d 909 (N.D. Cal. 2014) (the no-fly list). This Court

should confirm that the Fourth Amendment requires

probable cause—not mere reasonable suspicion—for

entry into a home.

II. A PROBABLE CAUSE REQUIREMENT FOR

HOME ENTRIES PRESERVES THE SANCTITY OF THE HOME.

The venerable notion that “[a] man’s house is his

castle” can be traced back to Magna Carta. Donohue,

6 Available at https://tinyurl.com/yz4euwr8.

8

supra, at 1251. The constitutional guarantee of security in one’s house was inspired by overbroad “general

warrants” issued by British colonial authorities. U.S.

CONST. amend. IV; Payton v. New York, 445 U.S. 573,

583 (1980). Nothing is nearer to the Fourth Amendment’s essence than preventing “the danger of needless intrusions” into homes. Payton, 445 U.S. at 586.

Because government officials can invade a home

without a warrant only in very rare circumstances, a

standard of mere reasonable suspicion undermines the

Fourth Amendment. “[R]easonable suspicion is a decidedly easy standard for the government to meet” and

could easily be used to justify routine, warrantless

home entries. See, e.g., Carbado, supra, at 472. Accepting this would wrongly “disregard the overriding respect for the sanctity of the home that has been embedded in our traditions since the origins of the Republic.” Payton, 445 U.S. at 601; see also Boyd, 116 U.S. at

630 (“It is not the breaking of his doors, and the rummaging of his drawers, that constitutes the essence of

[a Fourth Amendment violation]; but it is the invasion

of his indefeasible right of personal security, personal

liberty and private property . . . .”); United States v.

Reed, 572 F.2d 412, 423 (2d Cir. 1978) (op. of Meskill,

J.) (“To be arrested in the home involves . . . an invasion of the sanctity of the home. This is simply too substantial an invasion to allow without a warrant, at

least in the absence of exigent circumstances, even

when . . . probable cause is clearly present.”). As the

Third Circuit has held, a “laxer standard” than probable cause “would effect an end-run around” the Constitution, making “all private homes—the most sacred of

Fourth Amendment spaces—susceptible to search by

dint of mere suspicion or uncorroborated information

and without the benefit of any judicial determination.”

9

United States v. Vasquez-Algarin, 821 F.3d 467, 480

(3d Cir. 2016).

Probable cause at least limits warrant exceptions

and preserves some Fourth Amendment protections. It

can help ensure that “exigent circumstances” does not

become a shorthand for unconstitutional invasions of

citizens’ castles. This would protect civilians, suspects,

and officers alike.

III. A PROBABLE CAUSE REQUIREMENT PROTECTS BOTH HOMEOWNERS AND POLICE.

Fourth Amendment requirements protect not just

property—they safeguard human life. As early as

1603, the Court of King’s Bench warned that the “destruction or breaking of any house” to effect an entry

could cause “great damage and inconvenience.” Wilson

v. Arkansas, 514 U.S. 927, 935–36 (1995) (quoting

Semayne’s Case, 77 Eng. Rep. 194, 196 (K.B. 1603)).

This Court, too, has repeatedly noted the importance

of protecting homeowners’ lives and limbs from the

perils of unnecessary home entries. In McDonald v.

United States, 335 U.S. 451, 452–53 (1948), a police officer jimmied open a woman’s bedroom window and

crawled inside to investigate an illegal lottery scheme

operated from her boarding house. The officer lacked

an arrest or search warrant, and this Court held that

the subsequent search was illegal. Id. at 452–56. Concurring, Justice Robert Jackson expressed concern

about the safety of the search at issue, predicting

“grave troubles” if police continued to carry out entries

cavalierly. Id. at 459 (Jackson, J., concurring). He considered the lack of injury to anyone a matter of “luck

more than [of] foresight.” Id. at 460.

10

Like Case, many homeowners keep guns or other

weapons at home for self-defense. When officers perform warrantless searches, they are initiating an encounter that is inherently dangerous for officers and

occupants alike. In recent years, news reports and social media have featured countless stories of violent

encounters between law enforcement and homeowners—sometimes due to entries at incorrect addresses,

overzealous policing, and mistaken identity.7 For example, if a woman “sees a strange man, in plain

clothes, prying up her bedroom window and climbing

in, her natural impulse would be to shoot.” McDonald,

335 U.S. at 460–61. For his part, “an officer seeing a

gun being drawn on him might shoot first”—but under

the circumstances, Justice Jackson wrote that he himself “should not want the task of convincing a jury that

it was not murder” by the officer. Id. at 461. The warrant requirement discourages “a method of law enforcement so reckless and so fraught with danger and

discredit.” Id.

Home entries cannot constitutionally rest on tenuous assessments. There is no textual support for the

reasonable suspicion standard, and as four justices

wrote in Ker v. California, “practical hazards of law

7 See, e.g., Peggy Lowe, Former KCPD Detective Violated Cameron

Lamb’s Rights, Federal Court Rules in Wrongful Death Suit,

KCUR (Sept. 18, 2024) (describing a case in which an officer

“kicked over a barricade to enter [a] backyard” without a warrant

and fatally shot the occupant), available at https://tinyurl.com/ywkvnh49; Emma Colton, Bodycam Footage Shows Police Fatally Shoot Armed Homeowner After Responding to Wrong

House, FOX 32 CHICAGO (Apr. 17, 2023), available at https://tinyurl.com/36h6mxad; Anthony Galaviz, Armed Homeowner Was

Victim Shot by Reedley Police Officer During Burglary Suspect

Hunt, FRESNO BEE (Sept. 15, 2021), available at https://tinyurl.com/9m55szaf.

11

enforcement militate strongly against any relaxation”

of requirements for home entries. 374 U.S. 23, 57

(1963) (op. of Brennan, J.).

Besides, what does reasonable suspicion of an

emergency even look like? The officers here claim to

have reasonably believed that Case required immediate emergency aid—yet they waited 40 minutes before

entering his house. Cert. Pet. at 9. The reasonable suspicion standard led the court below to unreasonably

find an exigency, despite the officers’ decision to delay.

CONCLUSION

The Fourth Amendment requires a warrant backed

by probable cause for nearly all home entries—a rule

that exists to safeguard life, limb, and property. This

Court should reverse the decision below.

........................................... Respectfully submitted,

Lee A. Steven

Americans for Prosperity

Foundation

4201 Wilson Blvd., Ste. 1000

Arlington, VA 22203

(571) 329-1716

lsteven@afphq.org

August 6, 2025

Matthew P. Cavedon

Counsel of Record

Brent Skorup

Christine Marsden

CATO INSTITUTE

1000 Mass. Ave., N.W.

Washington, DC 20001

(706) 309-2859

mcavedon@cato.org