A weekend homicide is under investigation in Waterloo. Police say 20-year-old Robert (Vincent) Robinson of Waterloo was shot to death as he was leaving a downtown bar around 2 A.M. yesterday. Officials say an altercation broke out as the crowded Uptown Lounge was being let out at closing time. Shots were fired during the fight, and Robinson was hit. He died a short time later at a Waterloo hospital. Police say they’re trying to sort out varying witness reports, and have made no arrests in the shooting. Officials aren’t sure if Robinson was the intended target or an innocent bystander. The shooting was the second outside a Waterloo bar in less than a week. Last Wednesday, someone fired shots at a cab, injuring the driver. Investigators don’t know if the two shootings are related.