The suit filed by Frank Kerrigan's family accuses the Orange County Coroner's Office of negligence, concealment and intentional infliction of emotional distress, among other claims.
County spokeswoman Carrie Braun said she can't comment on pending litigation but that the sheriff's department is conducting an internal investigation.
"The department extends regrets to the family of Frank M. Kerrigan for any emotional stress caused as a result of this unfortunate incident," she said.
The mix-up began when a man was found dead behind a Verizon store in Fountain Valley, about 40 miles (64 kilometers) southeast of Los Angeles.
Frank Kerrigan's father, who goes by the same name as his son, said the Orange County Coroner's Office told him the body was his son's.
When he asked whether he should identify the body, a woman at the coroner's office said - apparently incorrectly - that identification had been made through fingerprints. Another family member who talked to the coroner's office said a woman told her Kerrigan also had been found with his identification, according to the lawsuit.
Last May, Kerrigan's family buried a man.
Eleven days later, Kerrigan turned up at a family friend's house. The friend called Kerrigan's family to tell them he was alive.
The man the Kerrigan family had buried turned out to be a Kansas native named John Dickens, who had to be exhumed before he was cremated and sent to his mother in Kansas.
Both Kerrigan and Dickens were homeless and mentally ill.
Kerrigan's family also alleges that the body found at the Verizon store was neither Kerrigan nor Dickens.
The man found at the Verizon store was listed as weighing 250 pounds, according to a report by the Fountain Valley Fire Department obtained by attorneys representing the Kerrigan family and provided to The Associated Press.
Meanwhile Kerrigan weighs about 160 pounds, and the body that the family buried matched that size, said James DeSimone, the attorney representing the family.
The coroner's office "did not want to admit to their identification error and instead released a body that resembled Frankie with the belief that no one would care because the deceased were mentally ill and/or homeless," according to the lawsuit.
"There's no logical explanation other than a cover-up," Carole Meikle, Kerrigan's sister, said Tuesday. "It doesn't add up. The pieces don't fit."
More important than possible monetary damages, Kerrigan's father said the family wants answers.
"Something went way, way wrong and we need to get to the bottom of it, period," he said. "It's just not right. It wasn't right for my son. It wasn't right for other people's sons and loved ones."
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