An assistant sub-inspector (ASI) of police has been arrested after publicly shooting three people dead on Sunday,  including a woman said to be his wife and her son, in Kushtia.

The shootings took place at a market in the district town's PTI Road around 11 am. The victims were identified as Asma Khatun, 34, her son Robin, 7, and bkash agent Shakil Khan, 28.

Read: Khulna ASI held for raping India-returned woman in quarantine

The three were rushed to Kushtia General Hospital, where they were declared dead.

ASI Soumen Kumar shot Asma, who was with her son. He then gunned down Shakil. As the child tried to run away, the off-duty ASI caught him before shooting the boy dead.

As the locals came to the rescue, Soumen threatened them by raising his weapon. Later, people began attacking him with stones and brickbats.

Read: 2 die in Kushtia after inhaling toxic gas inside septic tank

The gun-wielding Soumen then threw down his weapon and locals took him into custody before turning him over to the police, according to Kushtia Model Police Station Officer-in-Charge Sabbirul Islam. "No case has been filed yet over the incident."

"ASI Soumen Kumar is from Magura and was assigned to Khulna's Fultala Police Station," he added.

Asma's brother Hasan said her sister was Soumen's second wife.

Read:Tensions spill over clash between AL factions in Kushtia; 25 injured

ASI Soumen went to Kushtia without any official authorisation and killed three people there, said Khulna Superintendent of Police Mahbub Hasan."The ASI was not on leave. He has been suspended and legal actions will be taken against him."

"Soumen is being questioned. During the primary interrogation, Soumen said Asma was his wife and Robin her son from her previous relationship. The ASI also said Asma was shot dead as he could not accept her extramarital affair. However, we are investigating all aspects of the situation," Kushtia Additional Superintendent of Police Mostafizur Rahman said.