The BBC reports that the suspect, Emrah Erdogan, is of Turkish origin but has acquired German citizenship. Kenyan police suspect that he entered Kenya from Somalia, where he had been fighting for militants of the Islamist terrorist group al Shabaab.
Al Shabab has become a significant threat to Kenyan national security, especially after the Kenyan government crossed into Somalia to help battle the movement last October.
Erdogan was one of four people being trailed by Kenyan police since the shopping center attack. He is currently being detained; there are no details yet on specific charges or a possible trial date.