The defendant, Innocent Ngendakuriyo, told judges in his first hearing before the Bujumbura High Court that he was not involved in the killings in Gatumba, near the capital Bujumbura, and close to the border with DR Congo.
On the night of September 18, heavily armed men in uniform burst into the Gatumba bar and ordered the customers to duck for cover, then opened fire indiscriminately.
"I didn't take part in the Gatumba massacre," the defendant told the court. "I was on a special mission because I had been recruited by senior police officials to set a trap for (rebel commander) Claver Nduwayezu, alias Mukono.
"I had to bring Mukono to Gatumba on September 18, where dozens of policemen were waiting to eliminate him, but they fired before we arrived and they killed the people in Gatumba."
Top security official implicated
The accused claimed the massacre's "sponsors" were top security official General Maurice Mbonimpa, deputy police chief General Gervais Ndirakobuca and the commander of a special police unit, Colonel Desire Uwamahoro.
"I know these senior officers, I ask the court to summon them here to confront us," Ngendakuriyo said repeatedly, insisting that he had met and talked by phone with the senior officers.
Public prosecutor Arcade Nimubona said he had questioned the security services and that "there is no evidence implicating them". The judges followed his advice and refused to summon them.
Defence lawyer Fabien Segatwa said the case against his client was based on "confessions extracted under torture" and asked that the officers be called at least as witnesses "to clear up all the grey areas."
Growing violence in country
Since Thursday, 20 defendants have appeared in court and all pleaded not guilty.
The trial, which opened in mid-October but was postponed until this month, has generated huge public interest. Victims' families, diplomats and dozens of journalists have packed the courtroom, while hundreds of people have crowded outside to listen to the proceedings over a PA system.
"We have been frustrated so far by the way the trial has gone. Today is a great day because we have begun to find out what actually happened that night," said Josephine Gakobwa, who lost a brother and a niece in the attack.
Growing violence in Burundi has sparked fears of a return of large-scale hostilities in the poor central African country where an ethnic-based civil war claimed nearly 300 000 lives between 1993 and 2006.