The terrorist group Revolutionary Struggle has claimed responsibility for the armed attack earlier this month which left a police officer in a critical condition, as well as firing at a riot squad bus in December and placing an explosive device outside the offices of Shell oil company in southern Athens in October. In an 11-page proclamation made available to the Pontiki weekly newspaper, which also published its previous statements, the group explained that the January 5 attack in which more than 30 shots were fired at three riot squad officers, leading to the injury of 21-year-old Diamantis Mantzounis, was a response to the fatal shooting of 15-year-old Alexis Grigoropoulos by a police special guard on December 6. «Our decision to strike the armed riot squad murderers on January 5 was a response to the murder of Alexandros Grigoropoulos and our choice to act in this manner was mainly political,» Revolutionary Struggle said in its proclamation. «We have decided to take on the regime's uniformed thugs, ready even to engage in an armed struggle with them,» the group added. Mirroring a practice adopted by Greece's most deadly terrorist organization, November 17, Revolutionary Struggle also described in detail the January 5 attack, claiming that one of the three officers cowered behind a car and failed to fire back at the two gunmen. It also claims that riot police sitting in a parked bus nearby failed to act, preferring instead to «save their skins.» The group also calls on other extremist organizations to take up arms and hits out at leftist parties and Exarchia-based anarchists. Pontiki was told the proclamation had been left in an abandoned house in the eastern Athens neighborhood of Kaisariani on Monday. Anti-terrorism officers are examining it for clues. Meanwhile, police officers are due to stage a protest rally in Syntagma Square at noon today to demand more support from political parties and the public in general. The gathering will coincide with a rally by leftist students outside the entrance to Athens University, prompting fears that there could be clashes if the two groups meet up.