By MICHELE McPHEE and BRIAN ROSS

An American college graduate from Boston, who has been on the run from the FBI for years, is suspected of joining ISIS and leveraging his computer skills to spread the Iraqi terror group's propaganda on social media, a senior law enforcement official told ABC News.

Ahmad Abousamra, a dual American-Syrian citizen, was born in France in 1981 but grew up in the upscale Boston suburb of Stoughton under the watchful eye of his father, who was a prominent endocrinologist at Massachusetts General Hospital. He attended the private Xaverian Brothers Catholic high school in Westwood up until his senior year when he transferred to Stoughton High. There he was on the honor roll, school officials said, and went on to make the Dean's List at Northeastern University.

But Abousamra's life changed drastically in 2004 when prosecutors say he and co-conspirators traveled to the Middle East with the goal of fighting and killing Americans in Iraq.

Once abroad, two alleged co-conspirators of Abousamra's, Tarek Mehanna and another unidentified individual, worked as effectively the "media wing" of al Qaeda in Iraq (AQI), a 2009 indictment against Abousamra and Mehanna says. AQI later would evolve into the Islamic State of Iraq and Syria (ISIS).

Digital Feature: Who Is ISIS?

ISIS Not as Dangerous to US as al Qaeda, Top Terror Official Says

Obama Suggests ISIS Must Be Destroyed (or Maybe Not)

Both eventually returned to the U.S. where Mehanna was arrested and later convicted. But after Abousamra was questioned by the FBI's Joint Terrorism Task Force in 2006, he fled the country for Syria. He was charged with terrorism-related offenses in 2009, and in 2013 the FBI added Abousamra to its Most Wanted Terrorists list.

The senior law enforcement official said it appears now that Abousamra may have taken up a similar job with ISIS as his co-conspirators had for AQI. Abousamra, the FBI says, has a "college degree related to computer technology and was previously employed at a telecommunications company."

"There continues to be a worldwide search for Abousamra and he will be pursued until he is found," another official, FBI Assistant Special Agent in Charge Kieran Ramsey, told ABC News. The government offers a $50,000 reward for information leading to his capture.

Terrorism observers have noted ISIS's media savvy, from viral meme-like postings and hashtag campaigns on Twitter to elaborate full-production videos - efforts that can multiply the perception of ISIS's breadth and power in Syria and Iraq.

"ISIS understands very well that in order for an act of terrorism to be effective, it needs to actually terrorize people," said Peter Neumann, Director of the International Centre for the Study of Radicalisation (ICSR). "The act of communication that follows the act of violence is almost as important as the act of violence itself."

Neumann, who said he was unfamiliar with Abousamra, said ISIS's success in spreading their message is in part thanks to English-speaking supporters, many based in Western countries, who are familiar with social media.

"If you do have a European language ability, if you have computer skills, if you are quite clever and you come join ISIS, you are likely to be used for social media output," Neumann said. "A lot of Westerners do not have formal military training, but they do have precisely those skills."

An official at the U.S. National Counterterrorism Center declined to answer ABC News' questions about any individuals he said the center may be tracking abroad, "especially Americans."

[This story has been updated to reflect that Abousamra was added to the FBI's Most Wanted Terrorists list in 2013, not 2012 as originally reported.]