Americans involved in Nairobi mall siege?

Al-Shabab, the terrorist group behind the attack, denies an American link but has successfully recruited U.S. citizens in the past

Are American terrorists involved in the ongoing siege in the Westgate mall in Nairobi, Kenya? It's a question now being investigated by the U.S. government.

That's because the organization behind the attack -- al-Shabab, an al Qaeda affiliate based in Somalia -- has long been known to have a strong presence in at least one American city: Minneapolis.

As Steve Kroft reported in May 2010 piece, Homegrown Terror, "By far the most troubling situation [of Americans aiding terrorist groups] is in Minneapolis, home to more than 50,000 refugees from Somalia. . . . Over the past two years, more than 20 young men have disappeared from their homes and turned up fighting in Somalia, with a terrorist group called al-Shabab."

In this excerpt from that 2010 report, Steve reports on al-Shabab's influence on young men in a Minneapolis neighborhood known as "Little Mogadishu."

Americans recruited by al-Shabab

One of al-Shabab's most successful American recruits is Omar Hammami, a U.S. citizen born to an American mother and a Syrian father. Growing up in Alabama, Hammami had no involvement in radicalism -- or even in the Muslim religion. He converted as a teenager and studied Islam under a local, controversial cleric.

Hammami became interested in Somalia several years later, after moving to Canada and marrying a Somali woman. Hammami and his new family moved to Egypt, but later ended up in Somalia as an al-Shabab fighter.

Hammami -- also known as Abu Mansoor Al-Amriki -- quickly rose through the organization's ranks, eventually becoming an al-Shabab spokesman and recruiter. He focused on recruiting young Americans with YouTube videos featuring radical rap songs.

Earlier this month, Hammami told Voice of America that he had left al-Shabab after nearly eight years with the group due to an argument with the group's leaders. It has since been reported that Hammami was killed just weeks ago by al-Shabab, yet those reports cannot be fully confirmed.

From Steve's 2010 piece "Homegrown Terror," here is more on Omar Hammami, one of al Shabab's most successful U.S. recruits.

Al-Shabab's powerful American recruit