The U.S. military has appointed Brigadier General Richard Formica, who previously investigated detention practices in Iraq, to probe the suicide bombing of a Mosul mess hall this week that killed 18 Americans. A spokesman for U.S. forces in northern Iraq said Formica's investigation into the attack, in which a man apparently dressed in an Iraqi military uniform blew himself up in a crowded dining hall, had already begun but had no timeframe. "He has been appointed as the investigating officer and he will investigate the attack as quickly and as thoroughly as possible, although he will also have as much time as needed," said Lieutenant Colonel Paul Hastings, who is based in Mosul. Responsibility for Tuesday's attack was claimed by Ansar al-Sunna, a militant group that has operated in Iraq since late 2003 and which is believed to have ties to al Qaeda. The blast killed 22 people including 14 U.S. soldiers, four U.S. civilian contractors and three Iraqi National Guards. Formica, an artillery commander, was previously in charge of an investigation into allegations of abuse of detainees by special operations forces in Iraq. That investigation overlapped with a probe into prisoner abuse at Abu Ghraib prison.