A crime punishable by death.
Source: U.S. Courts
An offense for which the maximum punishment includes the death penalty. In the military, these offenses include: mutiny and sedition; misbehavior before the enemy; subordinate compelling surrender; improper use of a countersign; forcing a safeguard; aiding the enemy; spying; espionage; hazarding a vessel; misbehavior as a sentinel (in wartime); murder (premeditated or while committing other serious offense); rape.
Source: Judge Advocate General
A crime that you can get the death penalty for committing.
Source: California Courts.