Shawn Tyson, 16, has been charged with two counts of murder Miami - AFP The US teenager charged with double murder in the shooting deaths of two British tourists in the state of Florida had been arrested nine days earlier on a weapons charge, police have said.James Cooper, 25, and James Thomas Kouzaris, 24, were killed at 3 am (0700 GMT) Saturday in the city of Sarasota, while on vacation. On Sunday, police arrested 16-year-old Shawn Tyson and charged him with two counts of murder. He lives close to where the British men were gunned down. "Shawn Tyson has a previous arrest on April 7th for aggravated assault with a handgun," Sarasota police said in a statement. Police and city officials held a news conference Monday but did not address how Tyson was back on the street after being arrested on a serious felony charge.Police chief Mikel Hollaway said at the news conference that investigators are still seeking a motive for the slayings. The victims were shot in a residential area near government-subsidized housing developments -- an unusual location for visiting tourists. "We have our suspicions but at this time it would be unfair to state those, so I will withhold comment," Hollaway said of why the victims were there. The men were on a family vacation and staying in Longboat Key, a nearby beach resort community. One of the victims' parents was traveling with them on vacation. "I think they were just friends," Hollaway said when asked about the relationship of the victims. "They both had recently graduated from college and they were in the United States celebrating," he said. As for the motive, he added: "No, because what we thought is not panning out, so at this particular point in time, we don't" have a motive.Police discovered the bodies of Cooper and Kouzaris after receiving a 911 emergency call early Saturday. "We will find out why this occurred and we'll prosecute the case thoroughly," the police chief said. Mayor Kelly Kirschner expressed condolences to the families of the victims. "The tragedy in terms of the loss of life of the young men, I don't think can be underestimated, embarking on their careers shortly after graduation from college," the mayor said. They were the first homicides in the city of Sarasota this year. "That's not the image of Sarasota," Kirschner said. "This is an anomaly. It's not something we take lightly."