Greek police have released CCTV footage of the deadly attack on neo-Nazi Golden Dawn's offices in northern Athens that left two of its members dead and one wounded.
The clip shows two men approaching the party's branch before starting the shooting spree and fleeing the scene. The man who survived by hiding into a building, named as Alexandros Gerontas, is thought to have come face to face with the assailants.
The gunman shot two of the victims in the head at point blank range. He was wearing a baseball cap while the other suspect was wearing a motorcycle helmet.
The two victims, identified as Manolis Kapelonis, 23, and Giorgos Fountoulis, 26, were described by Golden Dawn as "members of our family".
Police are investigating whether the killing may have been carried out in revenge against the murder of anti-fascist rapper Pavlos Fyssas by a supporter of Golden Dawn.
A police official said the shooting appeared to be a "terrorist attack".
Nikos Dendias, public order minister, said: "We will not allow our country to become a place to settle scores". He also expressed "sadness at the death of the young men".
Syriza party, the main left-wing opposition party, also condemned the shootings. "This murder creates a climate of instability and targets democracy," it said
Investigators fear that far-left and anarchist extremist groups, who have claimed responsibility for many shootings and bombings in recent years, may be responsible for the attack.
Counter-terrorism officers are focusing on a circle of suspects linked to the so-called Sect of Revolutionaries, a radical Leftist organisation who claimed responsibility for the killing of a police officer in 2009 by three gunmen and of an investigative journalist, Soktratis Giolas, in 2010.
Other guerrilla groups such as the Conspiracy of the Cells of Fire, may have launched a violence-based strategy to hit the Greek state, according to reports.
Following the killing of Giolas in 2010, the Sect of Revolutionaries vowed to transform the country into "a war zone of revolutionary processes, with arson, sabotage, fierce demonstrations, bomb attacks, armed killings" and they claimed to be "at war with our democracy".
Golden Dawn, which still remains Greece's third largest political force despite a dramatic drop in support after the government's crackdown, has reacted with anger at the deaths of its members.
"They were executed. If Greeks saw the images, they would be shocked," said the party's press spokesman, Ilias Kasidiaris.
"The criminals wanted to execute anybody outside the party offices," Golden Dawn said in a statement. "Before they drove off, the terrorists shot again at the boys lying on the ground. They literally emptied their weapons on them."
However, the mother of Gerontas made a heartfelt TV appeal to the Greek people to "overcome their differences" and to "stop the bloodshed".
Six Golden Dawn MPs faced charges of running a criminal organisation following the murder of the rapper, known as Killah P.
Three have been located in pre-trial detention in a high-security Athens prison, including party leader Nikos Michaloliakos.
Greek parliament cut off state funding to the far-right party in a vote that united left-wing and conservative parties.