The interior of this restaurant at the Ritz-Carlton hotel was badly damaged after an explosion on Friday morning. (Indonesian State Secretariat/Cahyo Bruri Sasmito/Associated Press)

A third bomb was set to go off in last week's hotel attacks in Jakarta but failed to detonate due to a timer malfunction, Indonesian police said Friday.

Ketut Untung Yoga, spokesman for Indonesia's national police, said a laptop filled with explosives and bolts found on the 18th floor of the J.W. Marriott was supposed to be the bomb detonated first in July 17 suicide attack.

"It is clear that the bomb found inside the hotel was equipped with a timer that shows the time of the (failed) explosion," Untung Yoga said. "It was supposed to explode before the other two."

Untung Yoga said the explosion from the device was likely meant to scare people to the ground floors where two suicide bombers detonated their explosive packs.

Seven people were killed and more than 50 people, including two Canadians, were injured after suicide bombers posing as guests attacked the J.W. Marriott and Ritz-Carlton luxury hotels in Jakarta last Friday morning.

Police had earlier confiscated handwritten notes, a cellphone and a bomb encased in a laptop computer from room 1808 of the Marriott, where the bombers had apparently prepared for the blasts.

The two bombers, believed to have been associated with the Southeast Asian militant network Jemaah Islamiyah, also died.

A hotel receptionist has told police the man who checked into the 18th floor room gave his name as "Nurdin." He gave a $1,000 cash deposit because he had no credit card.

Officials say they suspect the attacks were planned by Noordin Mohammed Top, a Malaysian fugitive who heads a breakaway faction Jemaah Islamiyah.

Noordin is accused of masterminding an attack on the same Marriott hotel in 2003 that killed 12 people, as well as a 2004 strike on the Australian Embassy that killed 10 and bombings on Bali in 2005 that killed 20.

Counterterrorism police have stepped up their search for Noordin and officials say a number of suspects have been detained in the investigation.

With files from The Associated Press