STAMFORD-A city man arrested six years ago for dropping more than 40 bags of crack cocaine in a bank, was arrested again in Stamford, this time for allegedly selling crack to an undercover officer in Stamford. Capt. Richard Conklin said police have been on the lookout for Terrence Mapp, 42, of William Street for some time after he was caught selling drugs to the undercover earlier this year. On Tuesday, police were told that Mapp was on a train to Stamford and officers set up at the Stamford train station and took him into custody at approximately 11 a.m.