In a statement, police said DNA found on the bomb sent to Itea police station, central Greece, "is identical" to DNA detected in a car used by Christodoulos Xiros to go into hiding while he was on prison leave earlier this year.
The 56-year-old has been on the run since January after being given nine days leave from prison. He was serving multiple life sentences for his role as a leading hitman for the November 17 group, which was broken up in 2002.
This group claimed responsibility today for the parcel bomb sent to the police station on April 29. The bomb was destroyed in a controlled explosion.
According to a statement posted on the Internet, the parcel bomb was sent in response to the murder of an Albanian convict, Ilia Kareli, who was beaten to death by prison guards in a Greek prison in March.
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Kareli died days after fatally stabbing a prison guard.
The statement posted on the web also expressed solidarity with the "wanted urban guerrilla Christodoulos Xiros".
While in prison, Xiros was allegedly in close contact with imprisoned members of the organisation, who are believed to have helped orchestrate his disappearance.
After disappearing in January, he resurfaced two weeks later with a self-made video calling for anti-government attacks.
"I've decided to fire the guerrilla shotgun against those who stole our life and sold our dreams for profit," he warned.
A booby-trapped car exploded outside the Bank of Greece in central Athens on April 10 as Greece was set to return to the debt markets after a four-year absence. Nobody was hurt.
Greece is offering a USD 5.4-million reward for the arrest of several wanted extremists, Xiros included.