Security has found bomb materials cached inside the Zone in the past. Obviously, getting in and finding a hidden bomb vest is a lot easier than sneaking in with one. Parliament members don't like the security inconvenience, and often refuse to be searched.

Look at the names of the people who were killed in the attack:

One of the lawmakers killed in the attack, Mohammed Awad, was a member of the moderate Sunni National Dialogue Front, according to party leader Saleh al-Mutlaq. A female Sunni lawmaker from the same list was wounded, he said.

A second Sunni lawmaker known to have been killed was Taha al-Liheibi, a key go-between in government efforts to negotiate with Sunni insurgents about putting down their arms and joining the political process.

Niamah al-Mayahi, a member of the Shiite United Iraqi Alliance bloc, initially was reported killed by Saleh al-Aujaili, a fellow member of the bloc. Later, al-Dabbagh's office said al-Mayahi was gravely wounded, but it was not immediately possible to reconcile the reports.

Nevertheless, it would be the second time in less than a month that a bodyguard wearing a suicide vest attacked a Sunni official. On March 23 a member of Deputy Prime Minister Salam al-Zubaie's security detail exploded his suicide vest and seriously wounded al-Zubaie, the highest-ranking Sunni in the Iraqi government.

Aside from the obvious media bonus, this is another part of the assault on moderate or pro-government Sunnis. The gas attacks have had similar targets.