BOSTON -- Drugs and alcohol did not play a role in the deaths of two Boston firefighters who died in a West Roxbury restaurant fire in August, according to a report released on Friday that was conducted by a Boston Fire Department inquiry board.

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But a top Boston Fire Department official said the board's report raises more questions than it answers. In a letter to city officials obtained by the Boston Herald, Boston Fire Department Commissioner Roderick Fraser cast doubt on his own department's report, saying investigators did not examine toxicology or autopsy reports and relied on firefighter interviews.

"Certain important avenues of investigation are not reflected in the report," Fraser wrote in a letter to Mayor Tom Menino and Deputy Fire Chief Steven Dunbar, who headed the Board of Inquiry probe. "Consequently, even as I receive this report with deep gratitude for the Board's prodigious efforts, I do so with great reservations."

Firefighters Paul Cahill and Warren Payne were killed last August in a fire at the Tai Ho restaurant. Autopsy results later showed that Cahill was legally drunk and Payne had traces of cocaine in his system.

On Friday, Dunbar defended the Board of Inquiry's report, saying there was no evidence that any impairment contributed to the men's deaths.

"We looked honestly to see if there was any indication that these members could perform their duties. We did extensive interviewing. We went over all the tactical strategy. We could not come up with any indication of any kind of impairment that would have led to their fatalities," he said.

In a statement, the head of Boston Firefighters Local 718, Edward Kelly, said he hoped "the matter will finally be concluded" with the release of the report.

He said the death of Cahill and Payne had been used to politicize ongoing negotiations between the city and fire department.

"While this makes for sensational headlines, it is a disgraceful tactic to smear the reputation of firefighters who sacrificed so much; and it does not make our city any safer," Kelly said.

In his letter, Fraser said that there is not enough evidence to prove that impairment didn't play a role.

"Although that may be the board's opinion, I do not believe that there is evidence to dismiss possible impairment," Fraser wrote. "I believe that this report leaves many unanswered questions."

The report also did not address why Cahill was not wearing his department-required face mask and why he didn't have his radio with him.

Mandatory drug tests have been a sticking point in the city and firefighters' union's contract negotiations.