WASHINGTON — The FBI made numerous serious errors in investigating allegations against former USA Gymnastics national team doctor Larry Nassar and didn’t treat the case with the “utmost seriousness,” the Justice Department’s inspector general said Wednesday.

The long-awaited watchdog report raises serious questions about how the Justice Department and the FBI handled the case and highlights serious missteps at the FBI between the time the allegations were first reported until Nassar’s arrest.

The inspector general’s investigation was spurred by allegations that the FBI failed to promptly address complaints made in 2015 against Nassar. USA Gymnastics contacted the FBI about the allegations in July 2015, but it took months before the agency opened a formal investigation.

At least 40 girls and women said they were molested over a 14-month period while the FBI was aware of other sexual abuse allegations involving Nassar.

Nassar was ultimately charged in 2016 with federal child porn offenses and sexual abuse charges in Michigan.

He is now serving decades in prison after hundreds of girls and women said he sexually abused them under the guise of medical treatment when he worked for Michigan State and Indiana-based USA Gymnastics, which trains Olympians.