Mehanna, who graduated from Massachusetts College of Pharmacy in May 2008, has been charged with conspiring to "provide material support and resources" for terrorists.
Authorities have been building a case for some time.
Mehanna had posted bail from a November 2008 arrest for lying to the FBI after agents interviewed him in December 2005, according to news reports. The FBI says he lied when questioned about Daniel Maldonado, a former resident of Methuen, Mass., suspected of traveling to Somalia to train in an Al Qaeda training camp.
Mr. Maldonado is now serving a 10-year sentence for training with Al Qaeda in Somalia. Mr. Abousamra fled the US in late 2006 after being interviewed by the FBI and is now living with his wife in Syria, the complaint says.
But Mehanna, too, was taking steps to become a terrorist by, among other things, traveling to try to find a terrorist training camp, the complaint says. Failing that, he returned home.
There were brief discussions among the group – which at one point included Maldonado and Abousamra. After the mall massacre plan fell through, Mehanna turned to the idea of becoming the "media wing" for Al Qaeda in Iraq. He established a website and became a blogger and disseminator of jihadist videos and other material, an affidavit in support of an FBI search warrant alleges.