Athens (AFP) - A four-year-old bid to jail members of Greece's neo-Nazi party Golden Dawn accused of murder, billed as one of the most important trials in modern Greek history, could be nearing its conclusion.

With a log of some 350 witnesses, more than 100 lawyers on both sides and a case file 1.5 terabytes in size, the "historic" trial that began on April 20, 2015, could credibly be completed by the end of the year, says prosecution lawyer Chryssa Papadopoulou.

"For the first time since the Nuremberg Trials, a political party stands accused of operating as a criminal organisation, with its members committing acts of violence," Papadopoulou told AFP at the Athens court of appeals where the trial is taking place.

With local and European elections upcoming in May, and national elections expected in October, the verdict will have heavy political implications -- Golden Dawn is the fourth largest party in parliament with an electorate of more than 300,000.

Party founder and leader Nikos Michaloliakos, a 61-year-old mathematician and Holocaust denier, and another 68 defendants face sentences of five to 20 years in prison.

Their main charge is participation in a criminal organisation, in addition to a host of other indictments related to murder and assault.

The catalyst was the September 2013 fatal stabbing of 34-year-old rapper Pavlos Fyssas, a self-declared enemy of the group, in the working-class district of Keratsini. His family said Golden Dawn had shadowed Fyssas and that he had been ambushed on orders from senior party brass.

On the night of the murder, witnesses said police stood nearby but did nothing as a large group of alleged Golden Dawn militants chased Fyssas and his friends. One of them grappled with the rapper and stabbed him in the heart.

"This is a criminal organisation. I want a maximum sentence on Golden Dawn," Fyssas's black-clad mother Magda, who had steadfastly followed the trial from the start, told AFP during a break in one of the sessions.

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On that day, the courtroom was nearly empty except for the three judges and prosecutor, a dozen lawyers and a handful of journalists.

The mother of one of the defendants was trying to persuade the court that her child "had done nothing wrong."

"He's 27 years old and lives with me. He has nothing to do with Golden Dawn, I'd know it if that were the case. He doesn't get involved in politics," the witness said.

- 'Key moment' upcoming -

Until Fyssas' murder, the police had not cracked down on the faction, despite years of growing concern over its campaign of violence against migrants and political opponents such as Communists.

Two other crimes are now part of the trial: the beatings of four Egyptian fishermen in 2012 and a group of Communist unionists in 2013.

"The key moment of testimony from the defendants approaches," says prosecution lawyer Thanassis Kampayannis.

Time was lost in deliberations on finding a big enough venue for the trial, and in a nine-month lawyers' strike in 2016.

Part of Golden Dawn's inner circle, including Michaloliakos, were placed in pre-trial detention following Fyssas's murder.

But after their maximum allowed imprisonment period of 18 months ended in 2015, they have never set foot inside the courtroom.

Their lawyers have consistently dismissed the charges as "political persecution" and an anti-nationalist "plot".

The party denies all neo-Nazi affiliation and acts of violence, claiming instead to be nationalist.

But the prosecution says evidence gathered on the party's activities is irrefutable.

"We have proven not only that these incriminating acts took place, but they were also carried out by a criminal organisation with a hierarchical structure... and National Socialist ideology," Kampayannis said.

Founded in the mid-1980s by Michaloliakos, Golden Dawn for years glorified Adolf Hitler and the warrior ethos of Nazi Germany.

Formerly on the fringe of Greek politics, Golden Dawn went from 19,000 votes a few years ago to over 426,000 in 2012 when it entered parliament for the first time after pledging to "scour the country" clean of illegal immigrants.

It confirmed these numbers in 2015, picking up nearly 380,000 votes.

Today it is the fourth largest party in the Greek parliament, with polls predicting it will secure nearly eight percent of the vote when the country goes to the polls later this year.

The city of Athens has denied Golden Dawn the use of public spaces for rallies in upcoming European and local elections.

Golden Dawn street attacks lessened considerably since Fyssas' murder, though they did not disappear entirely.

But deputy Athens mayor Lefteris Papayannakis notes that "whenever the party feels threatened, it makes its appearance on the streets to confirm its presence."