WASHINGTON (Reuters) - Under pressure to make public its case against a U.S. Army scientist in the 2001 anthrax murders, the FBI is preparing to release its evidence on the researcher, who killed himself before he could be charged, law enforcement officials said on Tuesday.

Bruce Ivins is seen during a 2003 award ceremony at the Pentagon . Under pressure to make public its case against a U.S. Army scientist in the 2001 anthrax murders, the FBI is preparing to release its evidence on the man, who killed himself before he could be charged, law enforcement officials said on Tuesday. REUTERS/USAMRIID/Handout

The evidence could be released as early as Wednesday and includes anthrax spores found in the office of Bruce Ivins that were linked through DNA matching to the spores sent through the mail, the officials said.

They said the evidence also included e-mails sent by Ivins that implicate him in the anthrax attacks, the worst biological weapon attack on U.S. soil.

The FBI plans to brief victims and their families on the latest developments, most likely on Wednesday. Court documents detailing the evidence against Ivins also would be unsealed, probably the same day.

Law enforcement officials have expressed confidence in their belief that Ivins acted alone and said they plan to close the investigation soon -- meaning there are no more suspects. But some scientists have questioned whether Ivins could have done it by himself.

Ivins, 62, was a microbiologist who worked on developing an anthrax vaccine and received a top Defense Department award in 2003 for his research at an Army facility in Fort Detrick, Maryland. He took an overdose of painkillers and died on July 29. His death has been ruled a suicide.

Attorney General Michael Mukasey declined to say whether the anthrax investigation had been closed by the Justice Department.

“The department has a legal and a moral obligation to make official statements first to the victims and their families and then to the public,” Mukasey said in Boston, adding that he hoped it would happen on Wednesday.

Paul Kemp, an attorney for Ivins, has said his client was innocent and that would have been established at trial. He noted that Ivins had cooperated with the FBI probe.

The anthrax-laced letters were mailed to media organizations and politicians shortly after the September 11 attacks by al Qaeda in 2001.

The mailings killed five people who caught the disease and sickened 17. The letters shut down a Senate office building and spread fear of further biological attacks among Americans already reeling from September 11.

The attacks severely disrupted the national postal service, forcing billions of dollars in operational changes, and turned ordinary envelopes into something to be feared.

Critics have questioned the evidence against Ivins, partly because FBI investigators mistakenly focused for years on another scientist at Fort Detrick, Steven Hatfill.

Hatfill never was charged and the government agreed in June to pay him $5.85 million to settle his lawsuit against the Justice Department.

Former Sen. Thomas Daschle, whose office as Senate Democratic leader received one of the anthrax letters, has expressed concerns about the investigation. He said the Ivins’ suicide further complicates the FBI’s ability to get all the answers.

Another critic, Sen. Charles Grassley, a Republican from Iowa, has vowed a thorough examination if the FBI closes its investigation into the attacks.