COLOMBO - Attackers opened fire on a prison bus outside Colombo on Monday, killing five prisoners and two armed guards in the worst gang-related violence to hit Sri Lanka in decades. Police said the gunmen sprayed bullets at the bus as it passed through a wooded area near the capital, also wounding four guards. One of the victims was a senior member of an underworld group operating in Sri Lanka, where automatic weapons remain easily available eight years after the end of a decades-long war. "It is believed that the shooting was a result of enmity between two underworld gangs," police said in a statement.