Federal authorities have already implicated Jack Strain in a kickback scheme while he was sheriff of St. Tammany Parish, but sources familiar with that probe say the FBI is investigating far more serious allegations — that the sheriff sexually abused a handful of teenage victims during his 20 years in office.

+8 Two former top deputies charged in St. Tammany kickback scheme plead not guilty Two men who served as captains under former St. Tammany Parish Sheriff Jack Strain pleaded not guilty in federal court Tuesday to taking part …

The probe into the sexual misconduct allegations began as FBI agents investigated the alleged bribery scheme at a Slidell work-release program that was privatized by Strain late in his tenure, which ended in June 2016.

At least one person said to have been victimized by the ex-sheriff was interviewed in late 2017, according to one of the sources.

The sources said at least four alleged victims — including both genders — have been identified by authorities. All were teenagers when the abuse occurred, though it's not clear whether all of them were under the age of consent, which is 17 in Louisiana.

In some cases, the sexual contact may have begun before the victim reached that age but continued for several years beyond it.

At least one victim has described the sex as not consensual, regardless of whether he was old enough to consent when the sex allegedly began. The victims have told authorities remarkably similar stories, according to one of the sources.

Strain's attorney, Billy Gibbens, declined comment on the allegations.

Strain has not been charged with any crime, though the bill of information charging former top aides David Hanson Sr. and Clifford "Skip" Keen hints strongly that federal prosecutors intend to also charge Strain in the alleged kickback scheme. Hanson and Keen are expected to plead guilty and cooperate with authorities.

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While the sex-abuse allegations are being investigated by the FBI, which also led the corruption probe, it's not clear precisely how much the sexual misconduct probe overlaps with the kickback scheme authorities have outlined.

There is at least some overlap: At least two of the alleged victims of sexual misconduct were employed at the work-release program at the center of the alleged kickback scheme, the sources said.

However, the two investigations are distinct in other ways, and if Strain is charged with sex crimes, the charges will likely be filed by 22nd Judicial District Attorney Warren Montgomery, not federal prosecutors, the sources said.

Because many years have passed since some of the alleged acts took place, prosecutors may have a limited number of charges available to them.

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Strain, 56, was chief of police in Abita Springs before becoming sheriff of St. Tammany Parish in 1996. Current Sheriff Randy Smith denied him a bid for a sixth term in a hotly contested 2015 election.

His political clout had begun to wane before that defeat, however. The candidate he backed for district attorney was defeated. Revelations that he had contracted with cronies to run two private work-release programs, both in lucrative no-bid deals, took some of the luster off his reputation.

A series of escapes at the work-release program in Covington did further damage, and he was forced to close it.

That program was operated by Marlin Peachey, Strain's longtime campaign treasurer. The other program, in Slidell, had been run by the Sheriff's Office before Strain decided to privatize it.

The company he hired to operate it was owned by the adult children of Hanson and Keen, high-ranking members of the Sheriff's Office who were close to Strain.

According to federal charging documents, the business took in about $1.2 million in just under three years — money that Brandy Hanson and Jarret Cole Keen shared with their fathers. Prosecutors also allege Strain got regular cash payments of more than $1,000.

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Hanson and Keen are lifelong friends of Strain from Abita Springs, where Strain has deep roots.

Strain was police chief of that town before running for sheriff. He was known in those days by the nickname "Booboo"; before he became the little town's top cop, he drove a school bus.

Married with two grown children, Strain has been closest to those he's known since childhood, including members of the large Hanson clan, several of whom he hired to work at the Sheriff's Office.

Katie Moore of WWL-TV contributed to this report.