Justin Givens, a Florida-based attorney, said Mary D. Knight's family alleges the Navy and Department of Veterans Affairs ignored red flags about the killer's deteriorating mental health.
"The gist of our lawsuit is there was a colossal (security) failure on behalf of the Department of the Navy and of the Federal Government and the Experts, the private security company used (by the government)," Givens said.
The lawsuit is being filed in Tampa, where Knight's younger sister lives.
"My sister would want me to fight for her and fight for the girls," said Patricia DeLorenzo.
Givens said the 34-year-old shooter, Aaron Alexis, had a well-documented criminal and mental health record that the Veterans Administration chose to ignore after visits to the facility earlier in the year.
"He told the VA something to the effect he was under attack. He told them he was having psychotic thoughts," said Givens. "I think it's fair to say the man did seek help."
Knight, 51, was a Seventy-First High School graduate, and the mother of two. She was working as an IT specialist in the Navy Yard when she was killed.
During a news conference Friday in Tampa, attorneys said they were seeking the money in an administrative claim. The claim, one of the first steps toward filing a lawsuit, has been delivered to the agencies.
Under federal law, the Navy and VA must investigate the claim and determine whether it has merit. If they think it doesn't, attorneys for Knight's family said they will sue.
Email and calls to the Navy were not immediately returned. A VA spokesman said he could not comment.