Fearing a threat to his son's life, slain Punjabi singer Sidhu Moosewala's father followed him with guards when he did not take his security men with him and witnessed the 28-year-old fall to a hail of bullets, according to an FIR.

Balkaur Singh, who took Moosewala and two others to a civil hospital on Sunday after the attack in Mansa district, said in his police complaint that his son would get threats to his life from gangsters for extortion. On Sunday, when he learnt that Moosewala had left home without his security guards or his bullet-proof vehicle, he went after him. The famous singer and Congress leader was shot dead by unidentified assailants on Sunday, a day after the AAP-led state government brought down his security cover from four Punjab Police commandos to two.

When Balkaur Singh reached Jawahar Ke village, he saw a Corolla car with four occupants trailing Moosewala's vehicle.

"After his son took a turn towards village Barnala, a Bolero vehicle with four youths stopped in front of his son's Thar," said the FIR.

The occupants of the Corolla and Bolero started indiscriminate firing at his son, Balkaur Singh said, adding that the assailants later fled.

He said many bullets hit his son. He took Moosewalla and the two other occupants to a civil hospital with the help of some locals but his son died, he added. The two others escaped with injuries.

Police registered a case of murder at the Mansa police station (City-1) after Balkaur Singh's complaint.

He said in the complaint that his son kept a bulletproof Fortuner after receiving threats to his life from the Lawrence Bishnoi gang and other gangsters. Yesterday, Moosewala went out with his cousin Gurpreet Singh and neighbour Gurwinder Singh, who were injured in the atack, without taking his two security men in his Thar vehicle.

Punjab Police has termed Moosewala's murder the result of an inter-gang rivalry and said the Lawrence Bishnoi gang was behind the killing.

At least three weapons were used and 30 empty cases recovered from the site.

Shubhdeep Singh Sidhu, who gained fame as Sidhu Moosewala, was left with two Punjab Police commandos after the state police withdrew two of four commandos from his security cover.

He was among 424 people whose security was withdrawn or curtailed by the Punjab Police on Saturday on temporary basis.

A case under various sections, including 302 (murder), 307 (attempt to murder) of the IPC and relevant sections of the Arms Act has been registered.

A three-member special investigation team (SIT) has been set up to probe the murder.