WASHINGTON (CNN) -- Former colleagues of Bruce Ivins, the man blamed for the 2001 anthrax attacks, accused federal agents Wednesday of hounding the government researcher and his family to the point where Ivins took his own life.
A source with knowledge of the case told CNN that federal agents searched Ivins' home in Frederick, Maryland, and questioned his children. They offered Ivins' 24-year-old son the $2.5 million reward for information about his father and showed his twin sister pictures of the anthrax victims, telling her, "Your father did this," the source said.
Ivins' former colleague, Jeffrey Adamovicz, said Ivins gave him a similar account of events.
"One of the statements that he relayed to me -- that his children were, in fact, told by FBI agents that were doing the interview that their father was a murderer," said Adamovicz. "And that I could tell greatly disturbed Bruce, as it would anybody."
But federal agents, who presented evidence Wednesday they said implicates Ivins as the lone culprit, defended their tactics and denied harassing the family.
"The notion that, somehow, these people were coerced by the agents or the lawyers is categorically false," said U.S. Attorney for the District of Columbia Jeffrey Taylor. "These agents handled themselves professionally, with great respect for Mr. Ivins and his family, and I'd say the same thing about the prosecutors in the case."
Authorities say Ivins, a 62-year-old Army biodefense researcher at the U.S. Army Medical Research Institute for Infectious Diseases in Frederick, Maryland, committed suicide last week as they were preparing to charge him with carrying out the anthrax attacks.
His lawyer denies Ivins was involved. The attorney and Ivins' former colleagues told CNN they think the pressure of the investigation led Ivins to kill himself -- an assertion federal officials dispute.
CNN's source with knowledge of the investigation said Ivins was a recovering alcoholic whose concern over the investigation led him to resume drinking this year. And though FBI officials deny harassing Ivins or his family, another researcher who got caught up in the investigation -- only to be exonerated -- described having been subjected to similar tactics.
"My girlfriend's home was also searched," said Steven Hatfill in July 2002 after being declared a "person of interest" in the case.
"She was manhandled by the FBI upon their entry [and] not immediately shown the search warrant. Her apartment was wrecked while FBI agents screamed at her that I had killed five people and that her life would never be the same again. She was terrified by their conduct; put into isolation for interrogation for eight hours," he said.
Federal officials did not respond to those claims, but they did settle with Hatfill two months ago for nearly $6 million.
In a written statement, Ivins' attorneys dismissed Wednesday's news conference in which a federal prosecutor declared Ivins the sole perpetrator.
"What the public demanded today was concrete evidence," said lawyers Paul F. Kemp and Thomas M. DeGonia. "Instead, it was deluged with everything but ... The government's press conference was an orchestrated dance of carefully worded statements, heaps of innuendo and a staggering lack of real evidence -- all contorted to create the illusion of guilt by Dr. Ivins."
They said hundreds of soldiers, scientists and family members showed up Wednesday to attend a memorial service for Ivins held at Fort Detrick.
"Dr. Ivins was characterized by his commanding officer for his 'openness, sharing, humor and curiosity' and was lauded for the central role he has played in the protection of the American soldier," his lawyers said in their statement. "No one who attended that service could believe that Dr. Ivins committed any crime."
Peter Hotez, chairman of microbiology at George Washington University, rejected the government's contention that Ivins' access to a sophisticated lab device called a lyophilizer -- used to dry anthrax -- was in any way damning.
And Richard Spertzel, a former colleague of Ivins at Fort Detrick, said there was "no way" a lyophilizer could have created the fine anthrax spores used in the 2001 letters.
In addition, Spertzel said, no one working at a U.S. government lab could have produced such high quality anthrax in secret.
CNN's Brian Todd contributed to this report.