NEW YORK — 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. Luigi 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. [time-brightcove not-tgx=”true”] Friedman Agnifilo’s law firm, Agnifilo Intrater LLP, confirmed in a statement late Friday that she had been retained to represent Mangione.