French police have released a photograph of one of the suicide bombers who blew himself up outside the national soccer stadium, appealing for any witnesses with information to come forward.
Investigators have already established that the man had been finger-printed by authorities on the Greek island of Leros on October 3 but his identity remains unclear.
Near to his body was a Syrian passport, which French investigators believe may have belonged to a Syrian regime soldier killed several months ago, a source close to the investigation told AFP on Tuesday.
When he entered Greece, the man was using the Syrian passport, with the holder later registered as crossing the border between Macedonia and Serbia where he formally applied for asylum, Serbian officials said.
Investigators have so far identified five of seven gunmen and suicide bombers whose bodies were found at three sites across the city, while the hunt is on for an eighth gunman who is believed to be on the run.