Records from the company that installed the hospital's water system show that, in December 2011, an inspection noted, "They have legionella" and "Systems are not being properly maintained."

Five months later, the same company -- LiquiTech -- concluded that the problems were continuing: "Obvious evidence that the systems had not been properly regularly maintained," the records say.

"They were not doing the monitoring; they were not doing the things critical to the efficacy of the system," said LiquiTech Chief Operating Officer Tory Schira.

He said his staff alerted hospital officials twice to the deficiency in their maintenance practices.

But he said there is no evidence that hospital officials fixed the problem and that the deaths "absolutely" could have been prevented had the system been maintained.

Schira's view was shared by Janet Stout, an authority on Legionnaires' disease who worked as a microbiologist at the hospital for 23 years.

"This outbreak was absolutely preventable," she said. Stout and her colleague, Dr. Victor Yu, pioneered the research on the ionization filtration system now used in hospitals nationwide.

But six years ago, the scientists' laboratory was closed by the hospital, which described it as "not productive" and "a drain on clinical resources."

The researchers, who left the hospital after their lab was shut, dispute that characterization. They said that, during the decade before their departure, hospital water had not been linked to a single case of Legionnaires'.

Had the laboratory remained at the hospital, the deaths of Bill Nicklas and others could have been prevented with the turn of a knob, Stout said.

"This is not, as they say, rocket science," she said. "This is straightforward."

A source told CNN that, about six months ago, the hospital did bring in a consultant who made recommendations about how to fix the water, but the VA apparently did not tell that consultant that the hospital had had any Legionnaires' cases. Had the consultant been told, the source said, the consultant's recommendations to the hospital would have been different. The source said it was not clear whether the hospital had followed any of the consultant's recommendations.

Last month, the federal Centers for Disease Control and Prevention sent a team to the Pittsburgh VA to investigate and make recommendations. Their findings are to be issued to the VA in the coming weeks.

VA spokesman David Cowgill would not agree to an interview. Instead, he released media advisories, one of which concluded: "VA is committed to providing safe facilities and quality care for veterans."

It added that an investigation was under way and tests had shown that remediation efforts had proven successful.

Outside his suburban Pittsburgh home, Bill Nicklas' flag still flies over his front lawn. He would have turned 88 last weekend, but instead of celebrating his birthday, his family held a memorial service. He leaves three sons, five grandchildren and a wife of 59 years.

The family has retained a lawyer and begun the process of filing a claim against the VA.

In the meantime, Sen. Bob Casey, D-Pennsylvania, and other members of Congress are calling for a full accounting of the outbreak.

The disease has long existed, but got its name in 1976, when an outbreak occurred among people attending an American Legion convention.

Some 8,000 to 18,000 people are hospitalized with Legionnaires' each year in the United States, according to the CDC.