Four migrant workers from Bengal — three from Murshidabad and one from Birbhum — died after they went down to clean a septic tank at an under-construction building in Mumbai, reportedly poisoned by the noxious gas in the chamber.

Although the incident occurred on Sunday afternoon, the state police came to know of it on Monday night. The bodies arrived at their respective villages from Mumbai on Tuesday before daybreak and were buried by 10am.

According to district police sources, when the state police received the news on Monday night, it was immediately conveyed to the respective chiefs in Murshidabad and Birbhum. The Murshidabad SP passed on the message to Nabagram and Baroa police stations. Local police officers were asked to reach out to the families of the victims.

Riyaz Sheikh, 20, Ziarul Sheikh, 36, were from Nabagram, and Imandar Sheikh, 38, was from Baroa. The fourth victim, Hasibur Sheikh, 24, was from Santhia in Birbhum.

Liaquat Sheikh, a Murshidabad resident who worked with them, said they had gone to Mumbai six months ago to work as labourers.

"They were working for a construction company at an upcoming building on Mint Road in Nagpara, Mumbai. The tank in the basement of the building was closed for three years. As the building work was nearing completion, the contractor ordered the tank to be cleaned.... On Sunday afternoon, two masons first went down to clean the tank. When those waiting outside heard their screams, three others went to rescue them. A rescue team and workers brought them out of the tank, unconscious. They were rushed to a local hospital, where doctors declared four of them dead," he said. "It seems the noxious gas claimed their lives."

"One of the workers, Burhan Sheikh, 31, is admitted to JJ Hospital in Mumbai. He is critical," he added.

A police source in Murshidabad said an accident death report had been filed in Mumbai and a probe initiated into the deaths.

Nurnahar Bibi, Imandar's wife, broke down in tears.

"I have three children who go to school. My husband was supposed to come home from Mumbai during Id. Unfortunately, his body came home 20 days before Id," she said, adding she had no idea how to fend for her children.

Asghar Ali, Riyaz's uncle, said: "If he worked here, he would have made ₹300 a day. In Mumbai, he was getting ₹800. He went to Mumbai in the hope of earning more money, but the accident claimed his life."