This week a 26-year-old American citizen of Somali origin from New Jersey was captured in Yemen after he tried to shoot his way out of a hospital, killing one guard and injuring others. Sharif Mobley was originally arrested in Sanaa, Yemen, in early March and held on charges that he was a member of Al Qaeda. He complained of being ill and was admitted to a hospital for about a week until the shooting episode.

The FBI is investigating Mobley's case, and was asking relatives about him before the shooting.

Sources say that Mobley had a relationship with Anwar Al-Awlaki, a former imam at the Dar al-Hijrah mosque in Falls Church, Va., who has been linked to a series of terror plots. Awlaki is considered an inspiration for Nidal Malik Hasan before the Fort Hood massacre and also is suspected of encouraging failed Christmas Day airline bomber Umar Abdulmutallab.

Mobley previously lived in Philadelphia and Newark, Delaware, where he occasionally worshipped at the mosque of the Islamic Society of Delaware. The Imam of the mosque, Abdel-Hadi Shehata, said Mobley moved to Yemen to learn Arabic and study Islam.

Old friends of Mobley said that he tried to convert them to Islam. One, Roman Castro, said Mobley called him a "'Muslim killer'" in 2006 after Castro served in Iraq.

Sharif Mobley is the latest case of an American who moved to Yemen to join Al Qaeda after becoming radicalized in the U.S. Dennis Blair, U.S. Director of National Intelligence, noted that Yemen is "'re-emerging as a jihadist battleground and potential regional base of operations for al-Qaeda.'"