A month after a nail bomb attack in Cologne injured 22 people and caused extensive damage, police on Friday arrested a 23-year-old man in the state of Hesse. Prosecutors and police interrogating the suspect, said he is believed to have been directly involved in the attack. The nail bomb was set off by remote control in Cologne's mainly Turkish Mülheim neighborhood on June 9. Since then, investigators have been searching for the perpetrator and a suspected accomplice, and had posted mug shots. An anonymous tip led investigators to the suspect arrested on Friday.