Speculation that the FBI may have triggered the blaze accidentally intensified, after the agency finally admitted last year it had fired potentially incendiary devices into the compound.
About 80 members of the Branch Davidian cult died when fire engulfed their compound in Waco, Texas, in 1993.
But in preliminary findings released on Friday, he said he had concluded with "100% certainty" that the FBI, and the US Government were not to blame.
"The tragedy at Waco rests with certain Branch Davidians and their leader David Koresh, who shot and killed four (government) agents, wounded 20 others, shot at FBI agents trying to insert tear gas into the complex, burned down the complex, and shot at least 20 of their own people, including five children," said the report from former Senator Danford.
Siege
The blaze broke out during as agents moved into the compound to end the 51-day siege.
Speculation that the FBI may have triggered the blaze accidentally intensified, after the agency finally admitted last year it had fired potentially incendiary devices into the compound.
Videotape of the events also appeared to show unexplained flashes.
But Senator Danford, who was appointed by Attorney-General Janet Reno, said on Friday he was certain government agents had not started the fire, nor opened fire on the Davidians.
He also said the government had not improperly used the military.
'No wrongdoing'
And he said there had been no government cover-up.
"There is no evidence of any wrongdoing on the part of Attorney-General Reno, the present and former director of the FBI, other high officials of the United States or members of the FBI hostage team who fired pyrotechnic tear gas on 19 April, 1993," he told a news conference.
During his inquiry, he hired a UK firm, Vector Data systems, to recreate some of the final day's events.
The firm said in its report that the flashes seen on the video were sunlight reflecting off debris, not security forces' gunfire.
The report comes a week after a jury in Texas also found that federal agents were not to blame for the deaths.
About 100 survivors and relatives of the dead had sued the government for $675m, alleging that agents had used excessive force to end the siege.
The deaths have sparked years of Congressional inquiries and criminal trials.
The government argued that Koresh taught his followers he was an incarnation of God and trained them for an armed apocalyptic conflict.
But surviving Davidians have insisted that their compound was a peaceful Bible study centre.