Mercer County Prosecutor Angelo Onofri announced his retirement Wednesday from an office he served for over 27 years. Onofri told his staff Wednesday he would retire on Aug. 1. He informed the governor of his decision via a letter on Monday. “It’s been a great career these 27 years,” Onofri told NJ Advance Media in a phone call late Wednesday. “I could not have asked for any better prosecutor’s office staff than the one we have in Mercer County.” Onofri joined the office in May 1998 and served in several capacities before former Prosecutor Joseph L. Bocchini Jr. named him first assistant in 20…