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 germ in an Army lab, a government scientist said today.

Using new genome technology to identify the type of Ames strain anthrax used in the attacks, the FBI began to focus on Ivins as its top suspect more than a year ago, according to the scientist who is close to the investigation.

Ivins “was the primary suspect for some time,” said the scientist, who spoke on condition of anonymity because he is not authorized to speak to reporters.

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

Five people died and 17 others were sickened by envelopes of anthrax sent through the mail in the weeks after the Sept. 11, 2001, attacks, spooking an already rattled nation. Ivins killed himself last week as prosecutors prepared to indict him on murder charges.

Although the Army biological weapons lab where Ivins worked — Ft. Detrick in Frederick, Md. — had long been on the FBI’s radar, scientists were unable to pinpoint the specific strain used in the attacks until recently.

The FBI recruited top genome researchers from across the country and gave them “no rules, so we could do the best and most compelling approaches,” said the scientist. At least $10 million was spent on the case, in what the scientist called “clearly the most expensive case FBI’s ever undertaken. And the most scientifically compelling case.”

The new genome technology used to track down Ivins was either not available or too expensive to use often until about three years ago.

Samples of cells taken from the bodies — and perhaps specifically from Bob Stevens, a 63-year-old tabloid photo editor in Boca Raton, Fla. — looked at the type of Ames strain anthrax that killed them.

Researchers then looked at DNA strands of the Ames strains and noted very subtle differences within them, the scientist said. Investigators then matched the strain found in the victims’ bodies to Ivins, who oversaw the Ft. Detrick labs that used it in research, the scientist said.