Transcript for FBI Hunts Boston Man, Believed in Syria
international manhunt for an American man and this question, is he the master mind behind so many of those Isis videos, the terror. He was raised here in America and here's ABC's chief investigative correspondent Brian Ross tonight. Reporter: For a group that seeks a return to the seventh century, Isis has become a master of 21st century social media. And tonight the hunt is on for an American who may have helped to create some of the graphic, gruesome videos of the battles, executions, even child recruits seen in new images today, all rolled out on Twitter, Facebook and other sites like some slick American media campaign. Isis understands very well that in order for an act of terrorism to be effective, it needs to actually terrorize people. Reporter: Which is why law enforcement officials now tell ABC news they are focusing on this former college student from Boston, Ahmad abousamra, believed to be one of the architects of the Isis social media strategy. He was put on the FBI's most wanted terrorist late last year with this description posted online. He is 5'10", slim build with a high-pitched voice and this is an excerpt of him speaking. Listen to a recording of his voice. They don't have a warrant, they don't have a right to do that. Reporter: Abousamra grew up in Boston, the son of a prominent doctor. An honors student at a catholic high school, abousamra went on to northeast university, where he studied computer technology, the very skills authorities say he's using now. The internet campaign authorities say he helped engineer with its horrifying images has been vital to the ability of Isis to capture the world's attention and win new recruits from the U.S. And elsewhere. It has actually energized their base. They feel that they are finally in a confrontation with the United States of America. Reporter: And that is exactly what the FBI says he wanted to do when he fled this country and became a fugitive in Syria, fight and kill his fellow Americans, David. Brian Ross on the possible home grown terror, Brian, thank
This transcript has been automatically generated and may not be 100% accurate.