THIS IS INTERESTING — and troubling:

American investigators looking into the suicide bombing of the United Nations compound on Tuesday are focusing on the possibility that the attackers were assisted by Iraqi security guards who worked there, a senior American official here said today.

The official said all of the guards at the compound were agents of the Iraqi secret services, to whom they reported on United Nations activities before the war. The United Nations continued to employ them after the war was over, the official said.

The official said that when investigators began questioning the guards, two of them asserted that they were entitled to “diplomatic immunity” and refused to cooperate. Diplomats working in foreign countries are often entitled to immunity from prosecution by local authorities, but the official said the two guards could make no such claim.

Well, that’s chutzpah. But why on Earth did the U.N. hire guys who had been spying on them as guards? I’m not the only one wondering:

Throughout the day, United Nations staffers came to gape at the wreckage of what had been their offices and to try to salvage the hard drives of their computers. Looking at the remnants of the office of Mr. Vieira de Mello, one woman gasped: “How could they have left this place so unprotected?”

The possibility that Iraqi security guards had cooperated in the bombing increased suspicions that Mr. Vieira de Mello was a target of the attack, the American official said. The truck pulled up to the wall just below his office while he was inside meeting with other American officials.

“We are very concerned about the possibility” that Mr. De Mello was chosen as a target, the official said.

The official said that the revelation that former agents of Mr. Hussein were still working at the compound had also added to their suspicions that it was loyalists to the deposed president who carried out the attack.

Maybe De Mello was looking too closely into where the “oil-for-food” money had gone? That’s a trail that probably goes beyond Iraq. Pure speculation, of course, but hard to resist on these facts.

UPDATE: Ted Barlow emails: “If you are _not_ suggesting that the U.N. bombed itself, you should probably make that loud and clear on your page.”

Huh? I really don’t see how Ted got that from this post, but in light of the great Ashcroft misunderstanding, I guess I should say that, no, I’m not blaming Kofi for conspiring to blow up the U.N. mission. Rather, I was suggesting (in agreement with Roger Simon) that there were a lot of unsavory go-betweens involved in the oil-for-food program, and that quite a few people might have had an incentive to foreclose further inquiries. Oh, and I don’t actually think that Frank J. is a communist, either. Though I don’t really mind if people get the wrong idea, there. And if you read my GlennReynolds.com post today, you’ll see that I’m entertaining multiple theories, none of which implicate the U.N. institutionally.

MORE: Tim Blair rounds up questions, and finds someone who admires the attackers.