City officials would not say how much the company is charging and a copy of the contract between it and Jones & Mayer was not made available.
The city's decision to retain the firm was first reported Thursday by theOrange County Register.
City spokesman Bill Lobdell would not say why investigators were retained but issued a statement confirming that Talon was hired by the city's outside counsel. The statement also called "litigation support in anticipation of litigation — a common practice."
Pham's family, who live in Fountain Valley, has not yet filed any claims or lawsuits against Costa Mesa, but a small number of city officials have privately questioned the thoroughness of the police's investigation.
According to the police report, officers viewed about an hour of security camera video from inside City Hall leading up to Pham's death and didn't see him enter the building. They also searched his car but didn't find anything.
A toxicology report from the Orange County coroner's office later showed Pham had cocaine in his system at the time of his death, but experts couldn't say how it affected him at the time.
The report did note that "detectives' found no notes, documentation or further evidence indicating Pham had intentions of taking his life by committing suicide."
Pham, a city maintenance worker, had been on leave for months after injuring his ankle while hiking. His supervisor, Doug Lovell, speculated that Pham may have gone to City Hall to pick up paperwork related to applying for a contractor's license.
Pham was one of more than 200 employees slated to receive a notice that day that their jobs would be outsourced in six months as part of citywide austerity measures.