What Is 18 U.S.C. 13? The Assimilative Crimes Act

The Assimilative Crimes Act, codified at 18 U.S.C. § 13, lets federal prosecutors borrow a state’s criminal laws to charge conduct that happens on federal land when no federal statute already covers it. If you commit an act on a military base, in a national park, in a federal courthouse, or on similar federal property that would be a crime under the surrounding state’s law, you can be prosecuted in federal court under that state law. The state law applies as it existed at the time of the conduct, penalties included.¹

Where the Act Applies

The statute reaches anywhere within the “special maritime and territorial jurisdiction of the United States” defined by 18 U.S.C. § 7. That covers land the federal government owns or controls: military installations, national parks and forests, federal courthouses, Veterans Affairs campuses, Bureau of Prisons facilities, and similar properties. It extends to U.S.-registered vessels and aircraft operating outside any state’s jurisdiction, and to spacecraft on the U.S. registry while in flight.²

The type of federal jurisdiction over the land matters. Under exclusive jurisdiction, only the federal government can prosecute. Under concurrent jurisdiction, both sovereigns can. Under partial jurisdiction, the federal government has some authority while the state keeps powers like taxation. The Assimilative Crimes Act can operate under any of these three. It generally does not operate where the federal government holds a proprietorial interest only, because in those areas the state’s own criminal laws already apply directly and there is nothing to borrow.

The Gap-Filling Rule

The Act does not replace federal criminal law. It fills gaps. If Congress has already made your conduct a federal crime, the state law is not assimilated. Courts run a two-step analysis to decide.

First: does any federal statute already make the defendant’s conduct punishable? If not, the state law is generally assimilated. If so, the court asks a harder question: did Congress intend its federal statutes to occupy that field so fully that state law has no role? The Supreme Court set out this framework in Lewis v. United States (1998), refusing to assimilate Louisiana’s first-degree murder statute because the federal murder statute already addressed the killing and reflected a deliberate congressional judgment about categorizing homicide.³

The same logic drove Williams v. United States (1946). Arizona’s statutory rape law covered girls under 18, while federal law already criminalized carnal knowledge of a girl under 16 and adultery on federal land. Assimilating Arizona’s statute would have expanded the federal offense, so the Court blocked it.⁴

State Laws That Clash With Federal Policy

Even when a genuine gap exists, courts will not assimilate a state law that conflicts with federal policy. A Department of Justice Office of Legal Counsel opinion put it this way: the statute is meant “to use local statutes to fill in gaps in the Federal Criminal Code where no action of Congress has been taken to define the missing offenses,” and it cannot override existing federal legislative judgments.⁵ Where a federal employee’s conduct is specifically authorized by federal law, a state criminal statute cannot be assimilated to punish that same conduct.

Criminal Laws, Not Regulatory Ones

The Act borrows state criminal laws, not regulatory ones. A state that prohibits an activity outright has enacted a criminal law. A state that permits the activity under a licensing framework has enacted a regulatory scheme, even if violations carry criminal penalties. The Supreme Court drew this line in California v. Cabazon Band of Mission Indians (1987), holding that bingo restrictions were regulatory rather than prohibitory because the state permitted bingo under conditions rather than banning it.⁶ The distinction shapes whether a given state statute qualifies for assimilation.

What Gets Charged

Most prosecutions under the Act involve conduct that is clearly criminal under state law but that Congress never specifically addressed for federal land. The recurring categories are drunk driving, assault, domestic violence, some drug possession offenses not fully covered by federal controlled substance laws, and traffic violations.

DUI on Federal Land

DUI on a military base or in a national park is one of the most common charges. Federal law lacks a comprehensive DUI statute, so blood alcohol limits, implied consent rules, and penalties come from the surrounding state. Congress added a specific subsection, 18 U.S.C. § 13(b), that treats any penalty a state imposes through judicial or administrative action for an impaired driving conviction as “punishment” under the Act. That includes license suspensions and administrative sanctions, though any driving restriction imposed under the Act applies only within federal territory.⁷

Section 13(b) also adds a federal enhancement with no state counterpart. If a child under 18 was in the vehicle when you drove impaired, the court can add up to one year of imprisonment. If the child suffered serious bodily injury, up to five years. If the child died, up to ten. These enhancements apply even when the surrounding state has no child-passenger enhancement of its own.⁷

Assault and Domestic Violence

Violent crimes on military installations often come in as assimilated offenses. Federal law covers simple assault under 18 U.S.C. § 113, but many states define additional aggravated assault offenses that don’t map onto the federal statute. Results vary. In United States v. Harris (10th Cir. 2021), the Tenth Circuit blocked assimilation of Wyoming’s felony aggravated assault statute, holding that the federal simple assault provision already covered the defendant’s conduct and that adding the state felony would rewrite the offense categories Congress had set.⁸ Domestic violence charges on bases can also be assimilated where the surrounding state has specific statutes and no federal provision covers the particular conduct.

Drug Offenses and Minor Charges

The federal Controlled Substances Act covers a wide range of drug crimes, which limits how often state drug laws get borrowed. Gaps still exist. Some states criminalize possession of substances or paraphernalia in ways federal law does not, and when the conduct happens on federal land, the state law can be assimilated. Trespassing, disorderly conduct, and certain property crimes round out the typical caseload.

How the Case Moves Through Court

A case under the Act is a federal case from start to finish. The offense comes from state law, but the prosecution is handled by an Assistant U.S. Attorney in a federal magistrate or district court. It usually starts with an arrest or citation by a federal officer, such as a U.S. Park Ranger or military police officer. You then appear before a federal magistrate judge who informs you of the charges and your rights.

From there, the Federal Rules of Criminal Procedure govern discovery, pretrial motions, plea negotiations, and trial. Because state substantive law rides on top of federal procedure, unusual arguments arise. The prosecution has to show that a genuine gap in federal law exists. The defense can challenge whether the state statute qualifies for assimilation or conflicts with federal policy.

Penalties and Sentencing

The Act requires “like punishment” to what the assimilated state law provides. That means similar, not identical. Federal sentencing law, including 18 U.S.C. § 3551, lists assimilated offenses among those sentenced under the federal sentencing framework.⁹ The state law sets the range of available prison time and fines; the federal judge applies those penalties within federal sentencing rules.

No Parole, Only Supervised Release

The federal system abolished parole for offenses committed after November 1, 1987, under the Sentencing Reform Act of 1984.¹⁰ Even if the surrounding state offers parole for the same offense, a federal court cannot grant it. The federal system uses supervised release instead, a period of community supervision that begins after a prison term ends.

The maximum supervised release term depends on the offense class: up to five years for a Class A or B felony, up to three years for a Class C or D felony, and up to one year for a Class E felony or a misdemeanor.¹¹ The Fifth Circuit confirmed in United States v. Flores (2025) that a federal court can impose supervised release on top of the state-law maximum prison term, because supervised release is not imprisonment and the “like punishment” language requires similarity, not perfect replication.

Fines and Restitution

Fine amounts generally track the assimilated state statute. A first-offense DUI, for example, might carry a maximum fine ranging from roughly $1,000 to $4,000 depending on the surrounding state. Federal judges retain discretion over fines and restitution, and federal collection tools include wage garnishment and Treasury offset.

Your Rights in an Assimilated Case

Because the prosecution is federal, you get the full set of federal constitutional and procedural protections regardless of what the surrounding state would do.

Jury trial under the Sixth Amendment, even for offenses that would be tried before a judge in state court.
Speedy trial under the federal Speedy Trial Act, which requires charges within 30 days of arrest and trial within 70 days of the indictment or initial appearance, whichever comes later.¹²
Court-appointed counsel through the Federal Public Defender’s office if you cannot afford a lawyer.
Fourth Amendment protections under federal standards, with evidence subject to suppression through pretrial motions.

One of the strongest defense angles is a challenge to the assimilation itself. If a federal statute already covers your conduct, the Act does not apply, and the government may have to proceed under a federal charge with different elements or penalties. You can also argue that the state law conflicts with federal policy, or that the location does not qualify as federal territory under 18 U.S.C. § 7.²

Expungement After a Conviction

Clearing a conviction under the Act is very hard. Federal law has no general expungement statute, and federal courts have held that they lack inherent authority to expunge valid convictions. The Second Circuit vacated a district court’s expungement order on that ground in Doe v. United States (2016), finding no jurisdiction to expunge records of a valid conviction.¹³

State expungement laws do not fix the problem. Even if the surrounding state would expunge the same offense in state court, a state expungement order does not touch federal criminal records.¹⁴ Narrow federal exceptions, such as the Federal First Offender Act for certain minor drug possession convictions by defendants under 21, apply only to specific offenses and are unlikely to cover most assimilated charges. For most people convicted under the Act, the conviction stays on their federal record permanently.