The suspect in the killing of UnitedHealthcare CEO Brian Thompson plans to challenge his extradition from Pennsylvania to New York, where he faces a charge of second-degree murder in connection with last week’s high-profile fatal shooting.

The suspect, Luigi Mangione, 26, was arrested on Monday and charged in Pennsylvania for allegedly possessing an untraceable “ghost” gun.”

“He has constitutional rights and that’s what he’s doing” in challenging the interstate transfer, his attorney, Thomas Dickey, told reporters in Pennsylvania.

He also plans to plead not guilty to the charges filed against him in Blair County, Pennsylvania, Dickey said. A Pennsylvania judge ordered Mangione, 26, held without bail on Tuesday.

The Manhattan District Attorney’s Office said it will seek a governor’s warrant to try to force Mangione’s extradition. New York Gov. Kathy Hochul said in a statement that she’ll sign a request for the governor’s warrant “to ensure this individual is tried and held accountable.”

Dickey said he anticipates that Mangione would plead not guilty to the second-degree murder charge in New York.

The attorney said he has limited information about the facts of the New York murder case but he conceded Mangione is “accused of some serious matters.” He added that Mangione is “taking it as well as he can.”

Mangione’s defense was on Tuesday given 14 days to file a formal challenge to the extradition. The suspect was shackled at the waist and ankles during the hearing at Blair County Court House in Hollidaysburg, Pennsylvania.

The judge ordered Mangione held without bail, returning him to the State Correctional Institution in Huntingdon, Pennsylvania, where he’s listed as inmate QQ7787.

ABC News’ Peter Charalambous and Josh Margolin contributed to this report.