BAGHDAD — Iraq detained dozens of security officials responsible for protecting the Baghdad district where twin suicide bombings this week killed 155 people, and authorities said Thursday they are trying to determine whether they were negligent or even had a role in the attack.

The blasts in the heart of the capital infuriated Iraqis, who question how the bombers could have driven their deadly cargo undetected through the multiple checkpoints that dot Baghdad. Prime Minister Nouri al-Maliki’s government, facing a January election, has been under intense pressure to restore a sense of security and show that the military and police are able to take over when Americans go home.