The attack against the parliament building in the Green Zone is probably indicative of previous activity in caching explosive inside the zone in preparation for a bombing campaign there. Following such a method it is not necessary to carry the explosives into the zone under heightened security conditions such as the ones imposed after the parliamentary attack. Vest explosive "packs" have been found in the past weeks. There must be more.
So far this week there have been two attacks on bridges across the Tigris within the city. Such operations require a lot of planning and access to the bridge for an extended period of time. The story that a truck bomb knocked that great big bridge down lacks credibility for me. I know how to knock down bridges and an un-tamped surface blast is unlikely to do it on a bridge that size. The idea seems to be to separate Shia pockets in the city preventing them from building a Shia "cordon" across the town.
The article linked to below continues the story. pl