WASHINGTON — The FBI mishandled child sexual abuse allegations even after enacting new protocols since its bungled investigation into Larry Nassar’s assault of young gymnasts, the Justice Department’s watchdog found in a report released Thursday.

Michael Horowitz, the department’s inspector general, found that 42 of 327 sexual abuse cases reviewed were plagued with serious problems — including a lack of coordination with local law enforcement and a failure to follow up on leads — that required immediate attention from the bureau.

In roughly half the cases reviewed in the audit, the inspector general found “no evidence” that the FBI’s investigators reported instances of sexual abuse to local, state and tribal authorities. That failure to coordinate with other law enforcement agencies also contributed to the long delay of an investigation into Nassar by the bureau’s field offices in Los Angeles and Indianapolis, according to the report.

Even as young athletes started coming forward in the summer of 2015, Nassar, the former national gymnastics team doctor, was not arrested until late 2016. Nassar abused at least 70 girls and women during that period. He is now in prison after molesting hundreds of his patients, including Olympic champion Simone Biles, under the guise of medical treatment.

Horowitz noted in Thursday’s report that a child continued to be abused by an adult a year after a complaint was made to the bureau.

Illinois Sen. Dick Durbin, chair of the Judiciary Committee, in a statement Thursday urged the bureau’s leaders to “answer for the inspector general’s grave findings” and said he would hold hearings this year to determine why they had not sufficiently improved their procedures.

“It’s shameful that the FBI is continuing to fail victims,” he added.

The inspector general’s audit covers Oct. 1, 2021, to Feb. 26, 2023. It is a follow-up to a scathing report in 2021 that found widespread failures in the Nassar case and recommended significant improvements to the bureau’s protocols and training procedures.

Horowitz cited significant improvements since then, praising the bureau’s cooperation and overall effort to comply with his previous recommendations.

But he identified several structural flaws that continue to hamper those improvements, most notably the high caseloads — 40 to 60 cases per investigator.

“It’s critically important that the FBI appropriately handle all allegations of hands-on sex offenses against children,” Horowitz said in a statement. “Failure to do so can result in children continuing to be abused.”

FBI officials, speaking to reporters Thursday, said the inspector general’s findings were consistent with the results of internal audits they have conducted in the wake of the Nassar case.

But they also claimed that most of the problems cited by Horowitz were technical paperwork issues. Relatively few had resulted in serious allegations falling through the cracks, they said, adding that new training protocols, which will be enforced in the next few weeks, will enhance improvements that have already been made.

Investigators have been swamped by the rise in child sexual abuse complaints and the lack of sufficient funding for new positions, they added.

John Manly, the lawyer for more than 200 of Nassar’s victims, said in a telephone interview that the report was further proof that the FBI had not been doing its job to protect children.

“The Larry Nassar scandal could happen again today,” he said, referring to the report of a child being abused even after a complaint was filed to the FBI. “I talked to some of my clients this morning, and they said it was like a gut punch.”

But Horowitz said the bureau should be doing more to address its shortcomings. He said that in 18 of the cases, he identified serious deficiencies that required “further action” by the FBI, not just added documentation.

One of the cases involved an allegation by an adult victim against an abuser who had perpetrated the crimes years earlier. It took the FBI about a year to aggressively pursue the lead, while the person meanwhile “allegedly victimized at least one additional minor,” according to the report.

The alleged attacker was charged in June 2023 with producing child pornography and child sex abuse.

In a letter to Horowitz, Michael Nordwall, an assistant deputy director of the FBI, said that most of the issues reflected a failure to “properly document” investigative steps that had already been taken.

Agents had moved “quickly” to address “the handful of cases” in which more substantive investigative issues had been found, he added.