( CNN ) -- 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 . William James Vahey killed himself in Luverne , Minnesota , last month , two days after a federal judge in Houston said authorities could search one of Vahey 's thumb drives that allegedly contained images depicting sexual assault on children , CNN affiliate KPRC reported . 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 . `` This is one of the most prolific alleged predators we 've ever seen , '' Houston FBI Special Agent Shauna Dunlap told the station . 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 .
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 .