"We have solved the July 11 bombings case. The whole attack was planned by Pakistan's ISI [Directorate of Inter Services Intelligence] and carried out by Lashkar-e-Taiba and their operatives in India," A.N. Roy, Mumbai's police commissioner said.
Roy said the ISI had begun planning the attacks in March and later provided training to those who carried out the bombings.
Pakistan said India had shown them no evidence of Pakistani involvement in the blasts which killed more than 200 people.
"India has always chosen this path of pointing fingers at Pakistan without evidence," Tariq Azim Khan, the information minister, said. "If they have any evidence, they should provide us evidence and we will carry out our investigations."
Fifteen people, including 11 Pakistanis, have been arrested over the attacks. They include an engineer, a journalist, a computer software professional and a doctor.
India suggested shortly after the attacks that they might have been carried out by a Pakistan-based group and postponed scheduled peace talks with Islamabad.
During a news conference, Roy gave a detailed description of how the explosives were transported into India and by whom. He also described how the bombs were packed into pressure cookers and placed on the trains.
Seven bombs exploded on crowded passenger trains during rush hour killing at least 207 people and leaving 700 injured.