Local and federal officials presented a united front yesterday in efforts to track down the source of deadly heroin in Pittsburgh, but they would not answer substantive questions about the ongoing investigation.

Led by U.S. Attorney Mary Beth Buchanan, the group made promises to combat the scourge of heroin laced with fentanyl, a potentially lethal painkiller, that is believed to be the cause of 44 overdoses -- six fatal -- throughout Allegheny County since Sunday.

The latest one tracked by Pittsburgh police occurred yesterday at 1:15 a.m. on the North Side.

"We are going to identify the source and supply of this deadly heroin," Ms. Buchanan said. "I can assure you, we are bringing to this problem every available resource."

Joining her were Pittsburgh Mayor Bob O'Connor, police Chief Dominic J. Costa, county Chief Executive Dan Onorato, county police Superintendent Charles Moffatt, and other representatives of the Pittsburgh police and U.S. Drug Enforcement Administration.

Pittsburgh police Sgt. John Fisher of the Weed and Seed task force, who attended the news conference, said it was not known how much of an impact the seizure in Pittsburgh of 1,131 stamp bags of the suspected deadly heroin has had. The problem, he said, is once the supply hits a city, it gets broken down into many smaller batches.

"It can go in 20, 30, 40 different directions, and the quantity can vary," Sgt. Fisher said.

City police made a major bust Monday, confiscating 1,050 stamp bags from one location. Narcotics Cmdr. Maurita Bryant refused to comment on any aspect of the bust, but sources said the seizure occurred at a stash house in the Hill District based on information obtained in Hazelwood.

Hazelwood is the location of two suspected fatal overdoses and seemingly a focal point of the heroin being sold under the brand name "Get High or Die Trying." Since the overdoses began, dealers have been laying low, according to police.

Ms. Buchanan said anyone prosecuted federally for selling drugs that cause a user's death could face up to life in prison.