Farrukhabad: A massive police force was deployed to rescue the children.
The man, who had taken 23 children captive at an Uttar Pradesh village, had apparently planned it over a month and studied similar cases of hostage crisis, police said on Saturday.
Subhash Batham, a murder accused, had taken the children hostage after inviting them to a birthday party at his house in Farrukhabad's Kasaria village on Thursday afternoon.
The children were freed after police barged into the house late on Thursday night and shot Batham dead.
"It seems Batham had planned it for a month," Inspector General of Police, Kanpur Range, Mohit Agarwal, told reporters, adding that his mobile phone has been seized.
Batham's wife, who was stoned to death by villagers, was involved in the incident and had demanded Rs 1 crore to free each child, he said.
Police have analysed Batham's phone and it has been found that he was "planning it for a long time, searching and downloading bomb making techniques", the officer said.
"He had studied in detail a similar case in 2004 in Russia where children were held hostage, besides some other similar cases," the senior police officer said.
The 40-year-old had earlier served 10 years in jail and was out on bail, Mr Agarwal said.
"He was in jail four months ago for robbery. It seems that he had planned this (the hostage taking) there, learning the fine details from other inmates. He collected arms and explosives with their help," he said.
Batham's mobile phone is being checked to find out who he was in contact with and the people he had met. Investigations are being carried out to ascertain if any one else was also involved in the incident, the senior police officer said.
The officer said that Batham had threatened on Thursday that he had bombs and had planted them in the his house''s basement where he was holding the children hostage.
"We tried to pacify him but he fired two shots and threatened to detonate the bombs," Mr Agarwal said, adding that locals kept him engaged as the police carried out the operation to free the children.
Locals saw Batham pouring some flammable material on the floor. This suggested that he was going to take a "major step", he said.
The Bomb Disposal Squad from Moradabad has seized a .315 bore rifle, a country-made gun, 20 live cartridges, 11 empty cartridges, one rifle round, 135 country-made bombs, cylinder bombs and material used for making bombs, the officer said.