An Ashburn psychology and psychiatry firm is partly to blame for the death of an infant who was allowed to have unsupervised visits with his father, a lawsuit filed Tuesday in Fairfax County contends.

The $20 million suit alleges that Ashburn Psychological Services and a staff psychologist were “wrongful, negligent and reckless” by concluding that Joaquin S. Rams, the father of 151 / 2-month-old Prince McLeod Rams, should be allowed to have unsupervised visits with the boy.

Hera McLeod, the boy’s mother, says she had fought against unsupervised visits for her one-time boyfriend. During an unsupervised visit Oct. 20, the infant was rushed to a Fairfax County hospital, where he died, according to police.

Authorities allege that Prince was drowned by his father, who had taken out more than $500,000 in life insurance policies on the boy, according to court documents. Joaquin Rams, 40, of Manassas has been charged with first-degree murder and is awaiting a grand jury hearing in Prince William County.

Hera McLeod, 32, said that the Ashburn firm’s report, produced by psychologist Margaret Wong, played a key role in a Montgomery County court’s decision to allow Joaquin Rams to spend time with their son without supervision.

“My way of going forward is to make sure my son didn’t die for nothing,” McLeod said during an emotional news conference at the District office of her attorney, Patrick M. Regan. “If my son was here and he was old enough to talk, he would have a problem with what [the psychologist] did.”

A spokeswoman for the Ashburn firm declined to comment. Wong did not return a phone call seeking comment.

Wong has a PhD in school psychology and specializes in autism-related disorders, according to her biography on the firm’s Web site. McLeod said that Wong should never have been assigned or accepted the case given that her area of specialty does not involve psychological evaluations of adults.

Previous psychological tests and run-ins with the law also should have been factors in Rams’s evaluation, according to the lawsuit, which also says that the psychologist relied too heavily on Rams’s own evaluation of himself.