The defense attorney representing Luigi Mangione, the suspect in the killing of UnitedHealthcare CEO Brian Thompson, said he has seen "no evidence" linking his client to the killing, adding that "a lot of guns look the same."

"Well, as I indicated yesterday, I have not been made aware of any evidence that links the gun that was found on his person to the crime so these are things that we're looking to see," his attorney, Thomas Dickey, said on ABC News' "Good Morning America" on Wednesday.

He added, "Today's another day. We're looking forward to beginning our inquiry as to what evidence may or may not be out there."

The suspect, who is 26, 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.

He 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, Dickey told reporters in Pennsylvania on Tuesday.

Police officials in New York have not said whether the gun recovered in Pennsylvania is considered a match for the one used in the killing last week, but said it looks similar and that it would undergo ballistic testing.

"A lot of guns look the same," Dickey said on Wednesday. "If you brought a gun in and said, 'Well, it looks like that,' I don't even know if that evidence would be admissible. So I would argue it wouldn't be given much weight."

He also cautioned that anyone speculating on the case should take the potential evidence "in its entirety," not taking pieces of writing or other evidence "out of context."

"People put out certain things, parts of different things," he said. "I think any lawyer involved in this situation would want to see it all."

Mangione 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.