Washington ? The murder weapon was a flask.

Army scientist Bruce Ivins was the anthrax killer whose mailings took five lives and rattled the nation in 2001, prosecutors asserted Wednesday, alleging he had in his lab a container of the lethal, highly purified spores involved and access to the distinctive envelopes used to mail them.

Making its points against Ivins, a brilliant yet deeply troubled man who committed suicide last week, the government released a stack of documents to support a damning though circumstantial case in the worst bioterror episode in U.S. history. The court documents were a combination of hard DNA evidence, suspicious behavior and, sometimes, outright speculation.

Ivins’ attorney said the government was “taking a weird guy and convicting him of mass murder” without real evidence. Republican Sen. Charles Grassley of Iowa called for a congressional investigation.

Ivins had submitted false anthrax samples to the FBI to throw investigators off his trail and was unable to provide “an adequate explanation for his late laboratory work hours” around the time of the attacks, according to the government documents.

Investigators also said he sought to frame unnamed co-workers and had immunized himself against anthrax and yellow fever in early September 2001, several weeks before the first anthrax-laced envelope was received in the mail.

Ivins killed himself last week as investigators closed in, and U.S. Attorney Jeffrey Taylor said at a Justice Department news conference, “We regret that we will not have the opportunity to present evidence to the jury.”

The scientist’s attorney, Paul F. Kemp, heatedly dismissed that comment.

“They didn’t talk about one thing that they got as result of all those searches,” he said.

Taylor, however, insisted the evidence would have been enough to convict.

The prosecutor’s news conference capped a fast-paced series of events in which the government partially lifted its veil of secrecy in the investigation of the poisonings that followed closely after the airliner terror attacks of Sept. 11, 2001.

Ivins was described in the documents as the sole custodian of highly purified anthrax spores with “certain genetic mutations identical” to the poison used in the attacks. When pressed, Taylor acknowledged “a large number of individuals, over 100,” had access to the substance.

Investigators also said they had traced back to his lab the type of envelopes used to send the deadly powder.

As for motive, investigators seemed to offer two possible reasons for the attacks: that the brilliant scientist wanted to bolster support for a vaccine he helped create and that the anti-abortion Catholic targeted two pro-choice Catholic lawmakers.

Noting that Ivins would have been entitled to a presumption of innocence, Taylor nevertheless said prosecutors were confident “we could prove his guilt to a jury beyond a reasonable doubt.”