An Ashburn psychology and psychiatry firm is in part 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 lawsuit alleges that Ashburn Psychological Services and a staff psychologist were “wrongful, negligent and reckless” by concluding that Joaquin S. Rams, the father of 16-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 and the father of the boy. During an unsupervised visit Oct. 20, the infant died after being rushed to a Fairfax County hospital, according to police.

Authorities allege that Prince was drowned by his father, who took out more than $500,000 in life insurance policies on his son, according to court documents. Joaquin Rams, a 40-year-old who lives in 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, had played a key role in the Montgomery County court’s decision to allow Joaquin Rams to visit with her son without supervision.

“My way of going forward is to make sure my son didn’t die for nothing,” said McLeod, during an emotional news conference at the District office of her lawyer, 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, the psychologist assigned to evaluate Rams, 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 she never should 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 included in Rams’s evaluation, according to the lawsuit, which said the psychologist relied too heavily on Rams’s own evaluation of himself.