Former longtime St. Charles Parish District Attorney Harry Morel is expected to plead guilty to a single charge of obstruction of justice in federal court Wednesday morning, bringing to an end a long-running inquiry into allegations that he sought sexual favors from female defendants in exchange for lenient treatment from his office.

The relatively mild charge — it’s a felony, but carries a maximum of three years in prison — belies the salacious nature of the allegations against Morel, 73, who left office in 2012 after 33 years as St. Charles Parish’s top law enforcement officer.

The court papers charging him say only that the former DA interfered with a grand jury investigation by telling an unnamed person — “Individual A” — to destroy photos that showed an improper meeting between Morel and Individual A, who was also a criminal defendant in his parish.

The individual is not named in the document, but she is believed to be Danelle Keim, a young St. Rose woman who was working with the FBI in its investigation of Morel when she died of a drug overdose in 2013. Keim wore a wire for the government on several occasions, and the charges describe Morel telling her to “get rid of” and “destroy” the photos.

Three years before her death, in early 2010, Keim had called 911 to report that Morel had come to her home and made an unwanted sexual advance. A few months earlier, the St. Charles Sheriff’s Office had captured a jailhouse call on tape in which Keim’s then-boyfriend, Errol Falcon Jr., who was serving time for burglary, told Keim he understood he would get more lenient treatment if she performed sexual favors for Morel.

There’s no evidence Falcon, who is serving a 15-year sentence, received any sort of break from Morel’s office.

The Sheriff’s Office has declined to release the 911 tape, citing the ongoing probe, but the resolution of the case may prompt the tape’s release.

It’s also possible that the government will divulge more about their case Wednesday. When a defendant pleads guilty, he must sign a document that summarizes the evidence against him, known as a factual basis; that document sometimes provides more details about the crime.

The case against Morel had appeared to be on life support after Keim’s sudden death. During interim U.S. Attorney Dana Boente’s tenure, federal prosecutors declined the case. But Kenneth Polite Jr. pledged that his prosecutors would take a fresh look at it.

Morel will enter his plea before U.S. District Judge Kurt Engelhardt.

Follow Gordon Russell on Twitter @gordonrussell1.