The suspect in the killing of UnitedHealthcare’s CEO has added a prominent defense lawyer to his legal team as Manhattan prosecutors work to return him from Pennsylvania to face a murder charge.Related video above: Suspect in UnitedHealthcare CEO murder fights extraditionLuigi Mangione will be represented by Karen Friedman Agnifilo, who was a high-ranking deputy in the Manhattan district attorney’s office for years before entering private practice.Friedman Agnifilo’s law firm, Agnifilo Intrater LLP, confirmed in a statement late Friday that she had been retained to represent Mangione. The firm said she will not be commenting on the case at this time.Mangione was arrested Monday after a customer at a McDonald’s in Altoona, Pennsylvania, saw him eating breakfast and noticed a resemblance to the person being sought by police in the Dec. 4 killing of Brian Thompson in Manhattan.Police say Mangione was found with a gun, mask and writings linking him to …