Mumbai Terrorists Planted Five Bombs and Used Sophisticated Timers to Detonate Them

They did say, however, that when they successfully defused the bomb found in front of the Taj they discovered ball-bearings inside, which were designed to act as shrapnel when the bomb exploded.

Around 8 a.m. Thursday, Anthony received another call, he said, this one mentioning a metal box found behind the Taj hotel, near the rear entrance.

"There was no attempt to even conceal the box," he said, noting that the bomb was "left in an area which was still very busy that morning. It was open to the public, and it was also the likely escape route for the hotel's hostages."

The box turned out to be similar to the one found near the front entrance of the Taj, he confirmed, saying that it, too, contained about 17 pounds of what appeared to be the same black substance.

More worryingly, both bombs contained sophisticated PDT timers -- programmable electronic timer-delay devices.

"Earlier bombs used in India contained mechanical, clock-type timers," Gawade said. "These timers are very advanced. You can effectively delay a bomb exploding for any length of time between eight minutes to six months.

"The only other time we have come across such timers in India is in Surat," he said.

In July, about 25 bombs were found in the western Indian city of Surat, some of which were hidden inside hoardings or placed near police outposts. "Those bombs didn't explode because of mechanical faults with the timer," Gawade said.

Worryingly, he added, there appeared to be no evidence of such faults with the bombs found near the Taj.

The bomb squad was able to determine the time set for the first Taj bomb to explode, approximately between 2:30 and 3 a.m. Thursday. "I think they wanted to blow up the maximum number of people, including security forces, media people, and any guests evacuated from the hotel," Anthony said.

Still, pictures of the bombs acquired by ABC News seem to show writing in Urdu on the timer device. But the writing is too faint to determine what it says.