TAMPA, Fla. — A recent college graduate who was charged in four slayings that terrorized a Tampa neighborhood over the past 51 days used the same gun in all of the shootings and targeted people near bus stops with "no apparent motive," a police chief said Wednesday.The crack in the case came Tuesday when Howell Emanuel Donaldson, 24, brought a bag with a loaded handgun in it to his job at a McDonald's and asked a co-worker to hold it while he went across the street, authorities said. Restaurant workers thought that was odd and when Donaldson left, they reported the gun to a police officer who was doing paperwork there, setting off an investigation that linked Donaldson to the shootings. Aside from matching shell casings at the shootings, authorities said location data from Donaldson's cellphone put him at the scene of at least three of the killings."The gun is what we needed," Police Chief Brian Dugan said at a news conference surrounded by family members of the victims.The arrest overnight brought relief to an anxious community worried about a serial killer.