Kali9/Getty Images(CAPITOL HEIGHTS, Md.) -- A 15-year-old boy was killed and three other people were injured when at least two gunmen opened fire on them Saturday evening inside a 7-Eleven store in Capitol Heights, Maryland, officials said Sunday. The teenager who was fatally shot was identified as De'Andre Johnson of Washington, D.C., according to the Prince George's County Police Department. A $25,000 reward is being offered for information leading to the arrest of the killers, police officials said. The shooting unfolded about 8 p.m. Saturday inside a 7-Eleven convenience store on...