Washington ? DNA taken from the bodies of people killed in the 2001 anthrax attacks helped lead investigators to Bruce Ivins, who oversaw the highly specific type of toxin in an Army lab, a government scientist said Sunday.

Using new genome technology, researchers looked at samples of cells from the victims to identify the kind of anthrax Ames strain that killed them, the scientist said. They noticed very subtle differences in the DNA of the strain used in the attacks than in other types of Ames anthrax.

Spores taken from envelopes used to mail the anthrax, as well as from the sites where they were sent, also were scrutinized.

With that, investigators linked the specific type of anthrax back to Ivins’ biological weapons lab at Fort Detrick in Frederick, Md., where he oversaw its use and handling for research.

“It had to do with the very specific characteristics in the DNA of the letters and what was in Bruce’s labs,” said the government scientist, who is close to the investigation. “They were cultures he was personally responsible for.”

The scientist spoke on condition of anonymity because he is not authorized to speak to reporters. A senior U.S. official on Sunday night confirmed the scientist’s account.

The scientific discovery gave the FBI its first solid break in one of the nation’s most high-profile unsolved crimes after years of pointing the finger at the wrong suspect. Combined with other evidence, the Justice Department is expected to close the case this week, concluding Ivins was the mastermind and sole criminal behind the attacks that killed five and sickened 17 others in the weeks following 9/11.

Ivins killed himself last week as prosecutors prepared to indict him on murder charges.

Dozens of other researchers in Ivins’ lab also had access to the type of Ames strain used in the attacks, the scientist said, meaning the DNA alone is not enough to prove his guilt.