HOUSTON -

Local FBI agents tell Local 2 Investigates they are working on a recent case of child sexual assaults that is one of the worst they've ever seen, involving more than 90 victims. The FBI says it's likely there are more victims that law enforcement doesn't know about and they want to reach out to offer victims' assistance to those who could now be adults.

"This is one of the most prolific alleged predators we've ever seen," Houston FBI Special Agent Shauna Dunlap told Local 2 Investigates.

The suspect, William James Vahey, 64, of South Carolina, killed himself after the FBI began an investigation.

Vahey was not from Houston, but Dunlap says it is possible he had contacts with children of Houston-area families. He has taught at American schools abroad in various countries for years.

The Houston FBI was called in to investigate images found while Vahey worked at the American School in Nicaragua. The FBI says images show Vahey sexually molesting children.

Houston agents with the Crimes Against Children Task Force are sometimes asked to assist law enforcement from other countries when U.S. citizens are suspected of committing violations of U.S. federal law.

Vahey was a teacher at the American Nicaraguan School in Pista Suburbana, Managua, Nicaragua from Aug. 12, 2013, until he was fired on March 11, 2014.

Court documents reviewed by Local 2 Investigates show Vahey admitted to a co-worker that he molested underage kids his whole life.

Before teaching in Nicaragua, Dunlap says he taught in London, England; Caracas, Venezuela; Jakarta, Indonesia; Dhahran, Saudi Arabia; Athens, Greece; Ahwaz and Tehran, Iran; Madrid, Spain, and Beirut, Lebanon.

Click here to see a timeline of where and when Vahey taught abroad.

Dunlap says records show he taught at the Saudi Aramco School in Saudi Arabia from 1980-1992. Saudi Aramco has a division located in the Houston area and Dunlap says children from Texas may have attended that school while their parents worked in Saudi Arabia.

"In addition to foreign nationals the schools were attended by the children of American diplomats, military personnel stationed overseas and other American citizens working abroad," Dunlap said.

"We have an obligation to reach out to his victims and offer them victims' assistance," Dunlap said. "This is quite a task because while his victims likely lived overseas they could be living abroad or in the United State now."

Vahey killed himself in Luverne, Minnesota, on March 21, two days after a federal court judge in Houston approved a search warrant for a thumb drive Vahey owned that allegedly contained images depicting child sexual assault. It's unclear why Vahey was in Minnesota.

The case unfolded after Vahey reported his maid was fired after she allegedly stole personal items from his house last November.

In March of this year, the former maid brought a USB thumb drive to the American Nicaraguan School and admitted she stole it, but said she was coming forward because of the child sexual assault images she saw on the drive. A school employee viewed some of the images and described them to local authorities who contacted the FBI, the federal search warrant says.

"These images depict minor males in various states of undress," court records allege. "The minor males appear to be asleep, unconscious or possibly drugged."

When a school employee confronted Vahey, court records show he said, "I was molested as a boy and that is why I do this. I have been doing this my whole life."

"Vahey further stated he, 'Never hurt any of the boys.'" Court records go on to say Vahey claimed the boys were completely asleep and he used sleeping pills.

It is unclear if the school did a background check on Vahey.

Vahey was required to register as a sex offender in California after pleading guilty to child molestation in January of 1970. He was a swim instructor at the time in Santa Ana, California, federal court records show.

He was sentenced to 90 days in jail. Court records show he registered only once in 1970 and never renewed his registration.

It was not immediately clear if California required him to register again or if law enforcement there pursued him.

It's not clear how Vahey was able to get hired by all of the international schools. We reached out to some of them, but have not yet heard back.

Click here to see a timeline of where and when Vahey taught abroad.

If you have information about the ongoing investigation regarding William James Vahey, or believe you may have been victimized by him, the FBI asks that you complete a confidential questionnaire or submit a confidential email. You can also contact your local FBI office or the nearest American Embassy or Consulate.

Have a story idea for investigative reporter Jace Larson? Email him or send him a message on Facebook.