The firm of Peters, Murdaugh, Parker, Eltzroth and Detrick was founded by Murdaugh's great-grandfather in 1910.
The filing says that, for several years, Murdaugh submitted false documentation to the firm and to clients that allowed him to funnel stolen funds into fraudulent bank accounts.
The law firm wants to know where the funds went and if any of it is hidden away.
Murdaugh's attorney, Jim Griffin, said in a statement: "This is a very sad development. Alex holds every member of the Peters, Murdaugh, Parker, Eltzroth, Detrick law firm in very high esteem. He has pledged his full cooperation to the firm."
Murdaugh surrendered last month to law enforcement to face insurance fraud and other charges after state police said he arranged to have himself shot in the head so that his son would get a $10 million life insurance payout.
Murdaugh's lawyer blamed his decision to try to die on a lonely highway on Sept. 4 amid deep depression and a drug addiction worsened by his discovery of the bodies of his wife and son, who were shot multiple times at the family's home on June 7. Those killings remain unsolved.
The 53-year-old was charged with insurance fraud, conspiracy to commit insurance fraud and filing a false police report.
Investigators said Murdaugh asked a previous client who he was buying drugs from to kill him with a shot to the head on Sept. 4 so his surviving son could collect a $10 million life insurance policy, authorities said.
TIMELINE: Key dates in Murdaugh family investigations
Murdaugh's lawyers said he had been in drug rehab for about 10 days after his law firm fired him over missing money that could total millions of dollars.
State police also open an investigation into him and his family over the death of a housekeeper and nanny who died in his home.
The woman's death certificate said she died from natural causes and it wasn't reported to the Hampton County coroner. But a wrongful death settlement for $500,000 said she was killed in a slip-and-fall at Murdaugh's home.
Murdaugh's father, grandfather and great-grandfather all held the office of solicitor in the area for more than 80 years and other family members were prominent civil attorneys in the region. Murdaugh himself was an authorized volunteer prosecutor supporting his father's cases, a relationship the office severed this month as Murdaugh said he was seeking rehabilitation for an oxycodone addiction.
It all started June 7, when Murdaugh found the bodies of his 52-year-old wife, Maggie, and their 22-year-old son Paul shot multiple times after returning to their Colleton County home after visiting his sick father.
Those killings remain unsolved, and Murdaugh's lawyers have said he is adamant he had nothing to do with their deaths.
On Sept. 3, Murdaugh was fired by the PMPED Law Firm which was founded by his grandfather after the firm determined he took money.
The next day, Murdaugh's lawyers said he decided to kill himself, but have someone else shoot him. Murdaugh gave Curtis Edward Smith a gun and they headed to lonely Old Salkehatchie Road. Smith fired one shot that only grazed Murdaugh's head, a State Law Enforcement Division agent said in a sworn statement.
Murdaugh was able to call 911 and his initial story was someone passing in a pickup truck shot at him as he checked a tire that was low on pressure. His lawyers said a week later he told them about the insurance scheme and they told state police.
Smith, 61, was arrested late Tuesday and charged with assisted suicide, assault and battery of a high aggravated nature, pointing and presenting a firearm, insurance fraud, conspiracy to commit insurance fraud, distribution of methamphetamine and possession of marijuana. He remains in jail and it wasn't known if he had a lawyer to speak on his behalf.
Along with the killings of Maggie and Paul Murdaugh and the shooting of Alex Murdaugh, the State Law Enforcement Division is also investigating the missing money, whether anyone tried to obstruct an investigation into a 2019 boat crash for which Paul Murdaugh was eventually charged and a July 2015 hit-and-run death in Hampton County.