NICETOWN - Authorities are searching for a man accused of opening fire on an undercover Philadelphia police officer Tuesday afternoon in Nicetown.Anthony Cromwell, 43, was reportedly being investigated on suspicion of narcotic sales by an undercover officer on the 4200 block of Clarissa Street just before noon.MORE: Plainclothes officer uninjured after exchange of gunfire in Nicetown, police sayPolice say Cromwell opened fire on the officer's vehicle and a brief gunfire exchange ensued.