FORT LAUDERDALE, Fla.—A homeless man with a history of random violence fatally stabbed a 14-year-old boy riding his bike during a chance encounter and without apparent motive, a Florida police chief said Thursday. Semmie Lee Williams, 39, was arrested Wednesday in Miami on first-degree murder charges for the Nov. 15 slaying of Ryan Rogers, whose body was found alongside an Interstate 95 overpass the next day, said Palm Beach Gardens Chief Clinton Shannon. The high school freshman and avid soccer player had gone out for an early evening bike ride and never returned home. Court records show Rogers was stabbed numerous times in the head. The records say Williams’ DNA was found on a pair of headphones at the scene and that Rogers’ blood was found on a bandana Williams had in his backpack when he was located. Investigators say Williams also matches the description of a man videotaped by …