UnitedHealthcare CEO killing latest: Luigi Mangione's lawyer has seen 'no evidence' linking gun to New York

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."

"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," attorney Thomas Dickey told ABC News' "Good Morning America" on Wednesday.

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

The attorney said Mangione is "taking it as well as he can."

Mangione, 26, plans to challenge his extradition from Pennsylvania to New York, where he faces a charge of second-degree murder in connection with Thompson's Dec. 4 outside a Midtown Manhattan hotel.

The Ivy League graduate was arrested on Monday in Altoona, Pennsylvania, 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 on Tuesday.

New York police have not said whether the gun recovered in Pennsylvania is considered a match for the one used in the Midtown killing, 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 plans to plead not guilty to the charges filed against him in Pennsylvania, Dickey said. A judge in Pennsylvania ordered Mangione 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 also plead not guilty to the second-degree murder charge in New York.

Mangione yelled to the press about "an insult to the intelligence of the American people" as he was physically dragged into the courthouse on Tuesday.

When Mangione was arrested on Monday, he had "written admissions about the crime" with him, according to the New York arrest warrant.

Mangione's writings, obtained by ABC News, were addressed to the "Feds" and said, "I do apologize for any strife of traumas but it had to be done. Frankly, these parasites simply had it coming."

He claimed that the U.S. has the most expensive health care system in the world, but ranks about No. 42 in life expectancy. He said UnitedHealthcare "has grown and grown, but as our life expectancy? No the reality is, these [indecipherable] have simply gotten too powerful, and they continue to abuse our country for immense profit."

Whether Mangione has a personal connection to UnitedHealthcare is unknown, NYPD Commissioner Jessica Tisch said.

A UnitedHealth Group spokesperson said in a statement that they hope the arrest "brings some relief to Brian's family, friends, colleagues and the many others affected by this unspeakable tragedy. We thank law enforcement and will continue to work with them on this investigation."

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