A Plymouth police officer injured Tuesday afternoon in a motorcycle collision on Samoset Street died several hours later at Massachusetts General Hospital, Police Chief Michael E. Botieri said at a press conference. The officer, Gregg Maloney, 43, who was married and the father of two teenage boys, was a 17-year veteran of the Plymouth Police Department and a member of the motorcycle unit since 2009, Botieri said. The cause of the crash that killed Maloney is under investigation, Botieri said. No other vehicles appeared to have been involved, although another motorcycle officer was riding alongside Maloney at the time of the accident.Todd Feathers can be reached at email@example.com. Follow him on Twitter @ToddFeathers.