Longtime Queens District Attorney Richard A. Brown died late Friday.
He was 86 years old.
Ryan was sworn-in as acting district attorney Saturday, sources told ABC News.
Brown was first appointed Queens County District Attorney in 1991 by then-Governor Mario Cuomo and stayed in office for nearly 28 years. He was re-elected for seven terms, Ryan's statement said.
Brown's office prosecuted a number of high profile New York City cases, including that of several police officers who shot Sean Bell, an unarmed black man who was killed after his bachelor party at a Queens strip club, which resulted in no convictions.
Most recently his office prosecuted and won a conviction against Chanel Lewis for the 2016 murder of Karina Vetrano, a 30-year old woman who was beaten, sexually abused and strangled while jogging near her home in Howard Beach, Queens.
Brown is survived by his wife Rhoda, and their three children.
Funeral services will be held on Tuesday at 11:30 a.m. at The Reform Temple of Forest Hills, 71-11 112th Street in Forest Hills, Queens.