They are called "homegrown terrorists," Western citizens highly prized by Islamic militant groups because they can move across borders and carry out attacks easier than people from Middle East or South Asian nations.

Two such people — one Canadian and one Australian — are believed to have been involved in the July 18 bus bombing in Bulgaria that killed five Israeli tourists and a Bulgarian driver, according to Bulgarian investigators. Interior Minister Tsvetan Tsvetanov of Bulgaria said the two were members of the Lebanese Shiite Muslim militant group Hezbollah, which in turn is linked to Iran.

Here are some examples of Western citizens who have been linked to terrorism both in their home countries or abroad in recent years: