Story highlights FBI: William James Vahey taught at private schools in 9 countries for 42 years

He's one of "the most prolific alleged predators we've ever seen," agent tells KPRC

Thumb drive allegedly contained images depicting sexual assault on children

FBI is asking potential victims to contact them or nearest American Embassy

An alleged child predator who taught at schools across the world for more than four decades may have more victims, and the FBI is trying to track them down, the agency's Houston bureau said Tuesday.

There were images of at least 90 victims, dating back to 2008, and the FBI is encouraging additional alleged victims to come forward. The images on the thumb drive allegedly belonging to Vahey showed boys, estimated to be between 12 and 14 years old, asleep or unconscious, the agency said.

The images had captions and dates referencing places that Vahey had previously traveled with students, the FBI said.

Vahey began teaching in private schools in 1972, the FBI says. He last taught at the American Nicaraguan School in Pista Suburbana, Managua, Nicaragua from August 2013 until March 11, two days before he committed suicide, KPRC reported.

The case came to law enforcement attention after Vahey fired his maid for allegedly stealing personal items from his home last year, KPRC said. In March, the ex-maid brought a stolen thumb drive to the American Nicaraguan School, saying she came forward because the drive contained sexual images, the station reported.

The FBI said that when Vahey was confronted with the images, he " reportedly admitted molesting boys throughout his entire life and said he gave the minors sleeping pills prior to the molestation."

He had residences in London and Hilton Head Island, South Carolina, and traveled extensively, the FBI said. He worked at schools in nine countries, teaching a variety of subjects and coaching boys' basketball. He regularly accompanied students on overnight field trips, the FBI said.

The schools where he taught are, according to the FBI:

-- American Nicaraguan School in Managua, Nicaragua (2013-2014)

-- Southbank International School in London, United Kingdom (2009-2013)

-- Escuela Campo Alegre in Caracas, Venezuela (2002-2009)

-- Jakarta International School in Jakarta, Indonesia (1992-2002)

-- Saudi Aramco Schools in Dhahran, Saudi Arabia (1980-1992)

-- American Community School in Athens, Greece (1978-1980)

-- Passargad School in Ahwaz, Iran (1976-1978)

-- American School of Madrid in Spain (1975-1976)

-- American Community School of Beirut in Lebanon (1973-1975)

-- Tehran American School in Iran (1972-1973)

Anyone who has information on Vahey and who believes he victimized them can send a confidential e-mail to HOvictimassistance@ic.fbi.gov or contact their local FBI office or nearest U.S. Embassy.