A man wearing a police uniform drove a car bomb inside the headquarters of police in Tikrit town on Thursday, setting off a massive explosion that killed at least 15 police and wounded 22 others, police and witnesses said. The blast occurred at one of the station's busiest times, when dozens of policemen were arriving to relieve colleagues who'd been working all night, Daham said. "He waited until the shift change, then he exploded the car," Daham said, adding the aim was "to kill as many as possible." Daham said the attacker was able to slip into the station undetected because he was wearing a police lieutenant's uniform. He blamed guards at the station's gates for allowing the bomber to enter without checking his papers or searching his vehicle. Twenty cars were set ablaze after the massive blast, sending clouds of smoke into the sky. An Associated Press photographer on the scene saw at least 10 charred bodies laying on the ground, which was splattered with pools of blood and bits of human flesh. Several ambulances raced to the blast site, ferrying casualties to a local hospital. Police Capt. Hakim Mohammed, part of a force protecting Tikrit's main hospital, where most of the casualties were brought, said 15 people died and 22 were wounded. Daham confirmed the casualty toll. Khalil Ibrahim of Tikrit hospital said all the dead and injured were policemen. U.S. troops sealed off the area immediately after the blast, preventing people from entering. U.S. forces also set up new checkpoints across the city, searching vehicles, residents said. U.S. Army Maj. Neil Harper confirmed the attack was a car bomb, but he had no other details.