Before New York can put Luigi Mangione, the suspect in the killing of a health insurance executive on a Manhattan street, on trial for murder, it has to get him back in the state.

Mr. Mangione, 26, was arrested on Monday in Pennsylvania, where he faces gun and other charges. Shifting him to New York’s custody would require that he be extradited, a formal step that Mr. Mangione can challenge in the Pennsylvania courts. And he has indicated that he will be putting up a fight, one that could take weeks to resolve.

Here’s what to know about the extradition process.

What is interstate extradition?

The concept is nearly as old as the United States itself, and is specified in the Constitution. Article IV Section 2 says that if a person is charged with a crime in State A and flees to State B, State B is obliged to hand over the fugitive at State A’s request. The rule is meant to prevent people from avoiding justice simply by crossing a state line.

(The United States also has agreements with some — but not all — foreign countries providing for international extradition of fugitives.)

Mr. Mangione is accused of murdering Brian Thompson, the chief executive of UnitedHealthcare, in midtown Manhattan last week. He’s facing the charge in Manhattan because that is where the crime occurred. But he was apprehended nearly 300 miles to the west in Altoona, Pa. At a hearing Tuesday afternoon, his lawyer said he would try to block the extradition of his client to New York.

How is extradition supposed to work?

To seek extradition, the governor of State A submits paperwork to the governor of State B, describing the crime and establishing that the person in question is in State B.