An anonymous caller revealed the location of an envelope at a central spot in Athens last month and claimed responsibility for the bomb attack by militants outside the Federation of Greek Enterprises building, near the parliament in central Athens last month.
The nighttime blast smashed windows in several nearby buildings, including a hotel, private apartments, and the embassy of Cyprus. Police had cordoned off the area following warning telephone calls.
Greek police are currently examining this envelope and according to reports on Monday the envelope contained a memory stick which is being examined by forensic experts.
For decades, militant anarchist and far-left groups have carried out bomb attacks, often targeting banks and offices of large companies