In his book The Prince of the Marshes, British politician and writer Rory Stewart recounts his experiences at the Canal Hotel on the day of the bombing.

I had wandered past the security point without anyone attempting to search me or ask my business.
The Iraqis coming in and out of the compound were good-humored.
I had said to my friend that things seemed pretty relaxed.
She had replied that the special representative was proud that Iraqis could approach the UN building – unlike in the Green Zone, whose barriers were a half mile from the main offices.

... I went to the canteen, where I sat from ten until two in the afternoon, talking to local NGO staff who came in to eat and use the Internet.
I particularly liked a Tunisian security advisor who had served in the Balkans and was worried about terrorists targeting the UN.

I left at two, intending to return later in the afternoon to use the Internet.
But when I came back at 4:30, a thick column of smoke was rising from either end of the building, families were screaming and pushing at a cordon of U.S. soldiers, and the woman who had served me my salad in the cafeteria was running toward us.
In my brief time away from the building, a suicide bomber had driven his truck up beneath De Mello's office window.

The explosion occurred while Martin Barber, director of the UN's Mine Action Service (UNMAS), was holding a press conference.
The explosion damaged a spinal cord treatment center at the hospital next door and a U.S. Army Civil-Military Operations Centre located at the rear of the Canal Hotel, and the resulting shockwave was felt over a mile away.

 The blast was caused by a suicide bomber driving a truck bomb.
The vehicle has been identified as a large 2002 flatbed Kamaz (manufactured in Eastern Europe and part of the former Iraqi establishment's fleet).
Investigators in Iraq suspected the bomb was made from old munitions, including a single 500-pound aerial bomb, from Iraq's pre-war arsenal.

The United Nations Office for the Coordination of Humanitarian Affairs Humanitarian Information Centre (HIC) for Iraq (UNOHCI) was located directly beneath the office of Sérgio Vieira de Mello, the UN High Commissioner for Human Rights, and suffered a direct hit.
Of the eight staff and one visitor in the office at the time, seven were killed instantly, but de Mello and Gil Loescher were critically wounded and trapped in debris under the collapsed portion of the building.
An American soldier – First Sergeant William von Zehle – crawled down through the collapsed building and worked to extricate the two men.
He was joined later by another American soldier – Staff Sergeant Andre Valentine – and the two men spent the next three hours trying to extricate the two survivors without benefit of any rescue equipment.
 Loescher was rescued after having his crushed legs amputated by the soldiers, but Vieira de Mello died before he could be removed.

According to Abu Musab al-Zarqawi, Vieira de Mello was specifically targeted in the blast.
The reason given by al-Zarqawi for targeting Vieira de Mello was that he had helped East Timor become an independent state (see the Indonesian occupation of East Timor).
Zarqawi said that Vieira de Mello had participated in the unlawful removal of territory from the Islamic Caliphate and was therefore a thief and a criminal.
In his book The Prince of the Marshes, British politician and writer Rory Stewart recounts his experiences at the Canal Hotel on the day of the bombing.
I had wandered past the security point without anyone attempting to search me or ask my business. The Iraqis coming in and out of the compound were good-humored. I had said to my friend that things seemed pretty relaxed. She had replied that the special representative was proud that Iraqis could approach the UN building – unlike in the Green Zone, whose barriers were a half mile from the main offices.
... I went to the canteen, where I sat from ten until two in the afternoon, talking to local NGO staff who came in to eat and use the Internet. I particularly liked a Tunisian security advisor who had served in the Balkans and was worried about terrorists targeting the UN.
I left at two, intending to return later in the afternoon to use the Internet. But when I came back at 4:30, a thick column of smoke was rising from either end of the building, families were screaming and pushing at a cordon of U.S. soldiers, and the woman who had served me my salad in the cafeteria was running toward us. In my brief time away from the building, a suicide bomber had driven his truck up beneath De Mello's office window.
The explosion occurred while Martin Barber, director of the UN's Mine Action Service (UNMAS), was holding a press conference. The explosion damaged a spinal cord treatment center at the hospital next door and a U.S. Army Civil-Military Operations Centre located at the rear of the Canal Hotel, and the resulting shockwave was felt over a mile away.
 The blast was caused by a suicide bomber driving a truck bomb. The vehicle has been identified as a large 2002 flatbed Kamaz (manufactured in Eastern Europe and part of the former Iraqi establishment's fleet). Investigators in Iraq suspected the bomb was made from old munitions, including a single 500-pound aerial bomb, from Iraq's pre-war arsenal.
The United Nations Office for the Coordination of Humanitarian Affairs Humanitarian Information Centre (HIC) for Iraq (UNOHCI) was located directly beneath the office of Sérgio Vieira de Mello, the UN High Commissioner for Human Rights, and suffered a direct hit. Of the eight staff and one visitor in the office at the time, seven were killed instantly, but de Mello and Gil Loescher were critically wounded and trapped in debris under the collapsed portion of the building. An American soldier – First Sergeant William von Zehle – crawled down through the collapsed building and worked to extricate the two men. He was joined later by another American soldier – Staff Sergeant Andre Valentine – and the two men spent the next three hours trying to extricate the two survivors without benefit of any rescue equipment.  Loescher was rescued after having his crushed legs amputated by the soldiers, but Vieira de Mello died before he could be removed.
According to Abu Musab al-Zarqawi, Vieira de Mello was specifically targeted in the blast. The reason given by al-Zarqawi for targeting Vieira de Mello was that he had helped East Timor become an independent state (see the Indonesian occupation of East Timor). Zarqawi said that Vieira de Mello had participated in the unlawful removal of territory from the Islamic Caliphate and was therefore a thief and a criminal.
Canal Hotel bombing