The shots fired at a bus carrying policemen earlier this week came from two rifles, tests have revealed, prompting authorities to consider the possibility that an existing or new domestic terrorist organization was behind the attack rather than an extreme anti-establishment group. Ballistic tests on the seven cartridge cases found by members of the anti-terrorist squad revealed on Thursday that the bullets, two of which hit the bus, had been fired from two different rifles, most likely Kalashnikovs. The shots were fired from a building on an abandoned firing range where the University of Athens’s residence halls, known as Panepistimioupolis, are located. One bullet blew out two tires on the bus while another struck the engine. No police officers were injured. Authorities now believe that at least two people were involved in the attack and that a third person was probably acting as a lookout for the gunmen. A source who wished to remain anonymous told Kathimerini that the incident is unlikely to have been the work of extreme anarchists or anti-establishment figures. Anti-terrorist officers are disregarding a claim of responsibility by a group calling itself Popular Action and are instead expecting those behind the shooting to issue a proclamation. Police are now focusing on the theory that the shots were fired by members of an existing terror group, such as Revolutionary Struggle, which fired a grenade at the US Embassy last year, or experienced urban guerrillas that have formed a new organization. Officers were presented with another unusual shooting to investigate yesterday after a Proastiakos suburban railway train carrying passengers through the southern suburb of Tavros was fired upon late on Thursday. One bullet smashed through a window but no passengers were hurt. It was not clear if a second shot had been fired at the train, which was traveling from Athens to Kiato, west of the capital. Police had not made any statements by yesterday night linking the shooting with Tuesday’s attack on the police bus or any other incidents since the death of 15-year-old Alexis Grigoropoulos on December 6.