COLUMBIA — An ongoing Statehouse corruption probe already has netted four lawmakers and cast a shadow over South Carolina politics, but the FBI's newly confirmed involvement could bring more powerful guns to bear as the investigation continues to grow.

The FBI's interest in the probe raises the possibility that the U.S. Department of Justice could become more involved, bringing with it additional investigatory resources, wider ranging criminal statutes and federal charges that carry heftier fines and lengthier jail times.

“It’s a whole new dimension if the federal government gets involved in this,” said John Crangle, a longtime government watchdog in South Carolina who wrote a book about "Operation Lost Trust," the 1990 FBI investigation that led to the conviction of 17 members of the S.C. Legislature.

Miller Shealy, a Charleston School of Law professor and a former assistant U.S. attorney, said FBI agents' presence at interviews doesn't guarantee that federal charges will be filed. The Justice Department could just be keeping an eye on the probe, he said. 

The FBI field office in Columbia declined comment on the agency's reported involvement in the ongoing investigation Tuesday. 

But if federal prosecutors step in, it would open up a whole new list of charges that are not available to special prosecutor David Pascoe, who has led the state grand jury investigation into the alleged political corruption since 2015. 

Depending on what evidence is found by investigators, law enforcement officials could use federal bribery, tax evasion, wire fraud, mail fraud, banking fraud, racketeering and money laundering laws to prosecute any alleged crimes, experts said. 

Bank fraud, wire fraud and mail fraud — what Shealy calls the workhorses of federal white-collar criminal crime — have been widely interpreted in federal courts, he said, making them easier to prosecute than some of the narrower state laws used in public corruption cases. The scope of that federal involvement is not known. The FBI has not responded to calls.

Crangle, currently the government relations director for the S.C. Progressive Network, questions whether the federal racketeering law, which applies to a pattern of illegal business activities, might be considered if investigators continue to scrutinize Richard Quinn & Associates, one of the state's most powerful political consulting firms that investigators have scrutinized. Investigators seized documents from the firm's Columbia office in March. 

That firm, which is run by Richard Quinn of Columbia, has represented insurance companies, electric utilities, the state's flagship university and the State Ports Authority, while employing an influential list of state lawmakers as campaign consultants. Quinn has not been charged as part of the investigation and has denied any wrongdoing. 

But Rick Quinn, his son and a longtime state lawmaker, was the most recent politician to be indicted by Pascoe for, among other things, allegedly acting as a lobbyist during his time in office. 

“If it is determined that the Quinn firm is a criminal enterprise, everyone tied up in it is going to be implicated,” Crangle said.

The federal law enforcement agency's cooperation with the investigation into alleged influence peddling, political malfeasance and the misuse of campaign finances was confirmed last week, as two former state officials revealed that FBI agents had sat in on State Law Enforcement Division interviews. 

The manpower that the FBI can bring to bear, however, may be even more important than any criminal charges the agency has at its disposal.

Compared with Operation Lost Trust, when more than 70 agents were deployed in South Carolina, Crangle said the grand jury investigation has been limited to Pascoe, three other state solicitors and a handful of SLED agents. 

“SLED is a good quality law enforcement agency, but they have limited personnel," Crangle said. "If the FBI wants to have 200 agents investigating the Ports Authority and the Quinns, they can bring 200 agents in.” 

The FBI's involvement in the case, Shealy said, also may remove any chance the probe will be dropped or sidetracked because of political or legal pressures brought to bear against Pascoe, who has twice had to defend his work in court. 

“I have to think to that the FBI is keeping one eye on this, because Pascoe is under pressure," Shealy said. "It is very clear to anyone who reads the paper that he is being resisted very strongly. And of course he is. He’s snooping around where the big dogs are and he should be. But they will bite you if they can.”

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Reach Andrew Brown at 843-708-1830 or follow him on Twitter @andy_ed_brown.