Luigi Mangione has hired veteran former New York City prosecutor Karen Friedman Agnifilo to defend him against murder charges on Friday, according to a statement Friday night from her law firm Agnifilo Intrater LLP.

Friedman Agnifilo served as the second-in-command in the Manhattan District Attorney’s Office from 2014 to 2021 under former DA Cyrus Vance. A biography on her law firm website says she played a lead role in prosecuting “high-profile violent crime cases,” including those involving mental health and cold case homicides.

“Karen Friedman Agnifilo has a three-decade background in criminal justice, litigation, and trials. Her practice focuses on criminal defense in state and federal courts, leveraging her extensive experience prosecuting serious violent crimes, including complex homicide cases, from accusation to investigation to arrest and trial,” her biography says.

“While serving in the Manhattan DA’s office, Ms. Friedman Agnifilo was also integral to creating the office’s Human Trafficking Unit, Hate Crimes Unit, Antiquities Trafficking Unit, Terrorism Unit, its Cybercrimes and Identity Theft Bureau, as well as working on the creation of Manhattan’s first Mental Health Court,” the biography continued.

Friedman Agnifilo is also a frequent television news guest and commentator and is a former legal analyst for CNN.

She is also the co-host of a weekly podcast on the Meidas Touch Network where she discusses emerging legal issues and litigation strategy that routinely has half a million listeners per episode, according to her biography. She is also the legal advisor for the television show Law and Order.

Meanwhile, law enforcement sources have told ABC News that writings seized from Luigi Mangione indicate he had been developing a fixation and increasing malice toward UnitedHealthcare and allegedly talking about harming its leader for months.

Some of the entries in the notebook seized from Mangione upon his arrest in Pennsylvania earlier this week had dates on them going back to mid-2024, the sources said.

That fixation would eventually evolve into an alleged plan to shoot that CEO, the sources said.

Some of the writings were diary-style, documenting how he felt, what he did that day, and also documented a desire to focus on his health and himself, and find his purpose, the sources said.

Then, as time went on — as Mangione allegedly fell out of contact with friends and family and grew increasingly isolated — some of his writings indicated a deterioration in his thinking and state of mind, illustrating a gradual build towards the alleged plan to kill UnitedHealthCare’s CEO at their “annual parasitic bean-counter convention,” sources said.

Mangione’s writings, obtained by ABC News, 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.”

“I do apologize for any strife of traumas but it had to be done,” he allegedly wrote. “Frankly, these parasites simply had it coming.”

Neither Mangione nor his parents received insurance through UnitedHealthcare, according to UnitedHealth Group.

Mangione, 26, is currently in custody at a Pennsylvania state prison after a judge denied bail on Tuesday.