An assault rifle believed to have been used in an attack on the headquarters of the junior coalition partner PASOK a few hours before voting began in European Parliament elections on Sunday may have jammed, causing less damage than the perpetrators had intended, police sources indicated on Monday.

The police would not confirm whether they had any leads on the assailants but suspicions were believed to be focused on convicted members of two domestic terrorist groups – Nikos Maziotis, the self-confessed leader of Revolutionary Struggle who has been at large since July 2012, when he violated the terms of his conditional release from prison, and November 17 convict Christodoulos Xeros, who absconded while on a furlough from Korydallos Prison in January.

Police launched an investigation on Sunday after two windows on the second and third floors of PASOK’s headquarters in central Athens were hit by bullets from a firearm.

Ballistics tests on the casings later revealed that the weapon that fired the bullets had not been used in a previous terrorist attack.

Shells collected from the premises are believed to have come from a 7.62-millimeter caliber weapon, possibly a Kalashikov assault rifle, according to unconfirmed media reports.