The confession by Ajmal Kasab bolstered India's charges that terrorist groups in neighboring Pakistan were behind the well-planned attack, and that it is not doing enough to clamp down on them. The attack in which 166 people died severely strained relations and put the brakes on a peace process between the nuclear-armed enemies.
As part of the confession, Kasab described how he sprayed automatic gunfire at commuters while a comrade hurled grenades inside a railway station during one of India's worst terrorist acts.
"I was in front of Abu Ismail who had taken such a position that no one could see him," Kasab told the court. "We both fired, Abu Ismail and I. We fired on the public," he said, speaking in Hindi.
Kasab, a Pakistani who had consistently denied a role in the November rampage, reversed himself without warning, shocking even his lawyer.
In a calmly delivered statement, Kasab described how the attackers were sent from Karachi, Pakistan, by four men some of them known leaders with the Pakistan-based Islamic extremist group Lashkar-e-Taiba.
They traveled by boat arriving Nov. 26 in Mumbai, where they unleashed three days of mayhem. The 10 gunmen, armed with automatic rifles and grenades, split into pairs and killed people at a railway station, a Jewish center, a hospital and two five-star hotels, including the Taj Mahal.
Seema Desai, an analyst at the Eurasia Group in London, said Kasab's assertions could "increase tensions between India and Pakistan."
"Most likely Pakistan will not give his statements much credence and will question the circumstances under which he changed his story," she said in an e-mail.
Kasab faces the death penalty if convicted on the charges of murder and waging war against the country.
As the 66th day of Kasab's trial started Monday morning, he stood up just as a prosecution witness was to take the stand, and addressed the judge.
"Sir, I plead guilty to my crime," said Kasab, 21, triggering a collective gasp in the courtroom.
After a debate on the legality of such a confession, Kasab's statement was recorded, and the judge said he would have Kasab sign each page of the document, which would be reviewed by his lawyer, formally reversing his plea from innocent to guilty.
Kasab said he and Abu Ismail went to the Chatrapati Shivaji railway station in a taxi and left a bomb in the vehicle.
"I went to the restroom and attached a battery to a bomb and put it in a bag. Abu followed me to restroom and I asked him what I should do with the bomb."
"'Let's see,' Abu told me," he said.
They moved to the railroad station hall, packed with commuters. Abu Ismail put the bag near a pillar and stood close to a wall where they began shooting at people. Soon, policemen joined the fight. The bomb never exploded.
"I was firing and Abu was hurling hand grenades ... I fired at a policeman after which there was no firing from the police side," Kasab said.
From the railway station, where they killed more than 50, the two went to Cama hospital. A few more were killed there. The pair then went to the Chowpatty beach in a hijacked vehicle where Ismail was killed and Kasab was captured after a shootout with the police.
Kasab was treated for wounds and has since been held in solitary confinement in Mumbai's Arthur Road Jail where the trial is being conducted.
The siege of Mumbai, India's financial and entertainment capital, ended Nov. 29 with troops storming the Taj Mahal Hotel where some gunmen were holding hostages. All attackers except Kasab were killed.
Kasab said his confession was not coerced. "There is no pressure on me. I am making the statement of my own will," he said.
As part of the confession, he told how he became involved with Lashkar-e-Taiba. He said he became unhappy with his low wages as a shop assistant in the town of Jhelum in Pakistan, and left for Rawalpindi with the intention of becoming a professional robber.
While attending a festival in Rawalpindi, he and a friend decided to seek out the mujahedeen, who they thought could help train them as bandits. They went to a local bazaar and were directed to the local Lashkar office, he said.
Before being sent to India, Kasab said he lived in a house in Pakistan's largest city Karachi for a month-and-a-half with 10 other young men. All of them were transferred to another home and taken to sea where they met four handlers.
One of them was an Indian, who taught the attackers Hindi, he said.
Kasab confessed after his capture, but later withdrew that statement, saying it had been made under duress.
Last week, the Pakistan government gave a dossier to India providing new evidence of Lashkar-e-Taiba's role in the attack, and naming Kasab as a participant.
Asked by judge M.L. Tahiliyani why he confessed now, Kasab said it was because the Pakistani government recently acknowledged he was a Pakistani citizen, dealing a blow to his defense.
"If Pakistan has accepted me as its citizen, then end this case and punish me for my crime," he said. "My request is that we end the trial and I be sentenced."
Tahiliyani said no immediate judgment would be issued and the trial will resume Tuesday.
Pakistan Foreign Ministry spokesman Abdul Basit declined to comment on Kasab's court admission, but events took those at the hearing by surprise.
"Everybody in the court was shocked the moment he said he accepts his crime. It was unexpected," public prosecutor Ujjwal Nikam said. "We have finally extracted the truth."
Kasab said he killed fewer people than the prosecution alleges. Nikam said the confession could be a ploy to try for a lighter sentence.
An Indian court issued arrest warrants in June for 22 Pakistani nationals accused of masterminding the attacks, including Hafiz Mohammed Saeed, the founder of Lashkar-e-Taiba and two other leaders of the group named by Kasab as being involved.