By Nic Robertson
London (CNN) - The man who foiled a Yemen-based al-Qaeda "underwear bomb" plot was a British man of Arabic origin, according to Mustafa Alani, director of security studies at the Gulf Research Center.
The agent had Saudi roots, lived for a long time in the U.K. and at some point fell in with jihadist sympathizers.
That made him an attractive target for Saudi counterterrorism agencies, which recruited him about a year ago, says Alani.
CNN's Nic Robertson has more from London.
Click the video player above to watch his report.