Iraq has detained dozens of security officials responsible for protecting the Baghdad district, where twin suicide bombings this week killed 155 people.
Authorities say they are trying to determine whether those officials are negligent or even had a role in the attack.
Furious Iraqis are demanding to know how the bombers could have made it past the multiple checkpoints that dot Baghdad.
Prime Minister Nouri al-Maliki's government is under intense pressure to restore a sense of security and prove the military and police are able to take over when the Americans go home.
A military spokesman says 11 army officers and 50 security officials have been taken into custody over Sunday's bombings. He says the investigation will determine whether they were simply negligent or actually helped the insurgents.
The spokesman says they've also arrested suspects. They include the military commander and the police chief of the district where the bombs went off. But the spokesman refused to give details about the other suspects.
The head of the Sunni political faction in parliament has called for greater openness in the investigation.
Al-Qaida's umbrella group in Iraq has claimed responsibility for the attacks.
And Iraqi officials say the blasts were carried out by the same network behind the August suicide bombings.