CCTV footage of Nabha jail, call records of jail officials were being studied.
The Punjab Police and security agencies are investigating the recent activities of the
five prisoners who escaped from the maximum security Nabha Jail premises on Sunday following a well-planned attack by unidentified armed men.
Police sources said CCTV footage of the jail, call records of jail officials and others and posts on social media sites were being studied to know the involvement of people in the sensational jailbreak.
Of the prisoners who escaped, Khalistan Liberation Force (KLF) chief Harminder Singh Mintoo was arrested in November 2014 as he returned to India from Thailand after being deported from there.
He was nabbed from the Indira Gandhi International (IGI) airport in New Delhi along with an aide after security and intelligence agencies tracked him.
Mintoo's aide Gurpreet Singh, also deported from Thailand, was also arrested.
Mintoo is wanted in several terror cases in Punjab. Police had claimed that Mintoo was planning terrorist strikes in the region.
"The KLF chief was wanted in 10 terrorist offences and his key aide Gurpreet Singh had been tasked to execute a conspiracy of assassinating Hindu leaders in 2013 which was foiled by Punjab Police," Punjab Additional Director General of Police (Intelligence) Hardeep Singh Dhillon had said then.
Punjab Police traced and located them in Thailand in co-ordination with central agencies. On November 7, they were brought from Thailand to New Delhi in co-ordination with Thai authorities and arrested.
Two Punjab police officers camped in Thailand for three weeks while tracking the terrorists there.
"It was established that Harminder Singh was using a fake Malaysian passport issued in the name of Gurdeep Singh (Passport A-22967012 issued in Ipoh, Malaysia) and a fake Malaysian ID Card No. 610320086949," ADG Dhillon said.
Mintoo was trying to revive and strengthen the KLF with foreign-based supporters. He visited Pakistan and later travelled to Italy, Belgium, Germany, France and other European countries for 11 months (June 2013 to May 2014) before coming to Southeast Asia.
The Punjab Police came to know about the conspiracy to eliminate Hindu leaders after sleeper cells were busted by the police in 2013-14.
Mintoo had close contact with Pakistan's Inter-Services Intelligence (ISI) officers.
Another terrorist, Kashmir Singh Galwadi, who was involved in an attack on a Punjab Hindu leader in Gurdaspur in 2013, also escaped. He was also associated with the pro-Khalistan movement.
Gangster Vicky Gonder, arrested in December last year, was suspected to be behind the murderous attack on another gangster, Sukha Kahlwan, near Jalandhar in January 2015. Kahlwan was in police protection and was being taken for a court hearing when the attack took place at Phagwara town.
Kahlwan was gunned down while the police personnel accompanying him failed to repulse the attack.
Gonder and other gangsters had been in the news for running the affairs of their gangs from inside Punjab jails and also using social media.
Gangster Gurpreet Sekhon, who also escaped on Sunday, led another gang which was involved in murder, kidnappings, extortion and highway robberies.
The other two gangsters, Neeta Deol and Vikramjit, were also involved in various crimes in Punjab and other places.