COVINGTON -- Federal investigators may have uncovered the sexual abuse allegations against former St Tammany Parish Sheriff Rodney “Jack” Strain when they began searching for a motive for an alleged kickback scheme involving a privately-run inmate work release program in Slidell.

Current Sheriff Randy Smith unseated Strain in a contentious election in 2015, two years after Strain had awarded a no-bid contract to two of his top deputies and closest friends, David Hanson Sr., and Clifford “Skip” Keen.

Smith has said federal investigators first approached him about the work release scheme when he was a candidate for the office. Later, Smith said it was clear investigators had uncovered even more disturbing allegations against his predecessor, that Strain had sexually abused at least four teenagers, possibly when they were underage.

“Federal investigators indicated they were also looking into the motive of why this public corruption bribery took place with the work release in Slidell and also possibly in Covington,” Smith said in an interview Thursday.

Federal prosecutors filed a bill of information against Hanson and Keen that outlined their view of the money flow: Strain gave the contract to run the work release to a company owned by Hanson and Keen’s children, St Tammany Workforce Solutions, and in turn, they cut Strain in on the profits in the form of cash payments.

As WWL-TV and partner newspaper the New Orleans Advocate first reported, multiple sources close to the case say investigators are also looking into whether Strain may have sexually abused four boys and girls when they were teenagers.

“Some of these alleged allegations occurred when these individuals were much younger, in their teenage years. How far back, I don't know. How many, I don't know,” Smith said.

MORE: Sources: Ex-St. Tammany Sheriff Strain investigated for sexual abuse of teens

Two of the alleged victims were employed by St Tammany Workforce Solutions, according to sources familiar with the case.

While the St Tammany Parish Sheriff’s Office is not directly involved in the investigation, Smith said his agency has been cooperating with the federal probe, providing documents and information when asked.

Smith said he thinks the case won’t end with Hanson, Keen, and ultimately, Strain.

“We know there are individuals who were in his inner circle in high-ranking capacities that may or may not had knowledge. Some were here, some not here anymore, and it was a close-knit group of individual that he allowed in his inner circle that may have been part of this,” Smith said.

While the investigations appear intertwined, sources say any sex abuse charges that may be filed against Strain would likely come in state court, with the corruption charges handled by the feds.

Smith said the St Tammany District Attorney has met with the FBI about the allegations against Strain, but a spokeswoman for DA Warren Montgomery's office would not comment on whether they are involved in the sex crimes investigation.

“This is very disturbing and shocking to me, but not only to me but this whole parish. When you have allegations of sexual abuse involving minors, it's sickening. It's very disturbing,” Smith said.

Former Covington Police Chief Tim Lentz is running against Smith for St Tammany Sheriff, and while both men worked under Strain, Lentz was Chief Deputy before he retired in 2013.

Lentz said Thursday he had “no clue” there were ever allegations of sexual abuse involving strain, calling the news “a complete shock.”

“The allegations need to be investigated fully and if they're proven, he needs to be held accountable," Lentz said.

It's a sentiment shared by many in St Tammany, as a law enforcement investigation into another top law enforcement officer in the parish continues to unfold.