Police said one of the attackers has been arrested for murder and probe is on to determine if the woman was raped before being killed.
The incident happened Saturday when the couple, working at a brick kiln in Barasat in North 24-Parganas district, was returning home.
"We are also looking if she was raped. Let the post-mortem reports come. We are also looking for four to five more suspects," said Superintendent of Police Sougata Sen.
The victim's family has claimed she was raped.
Officers of state Criminal Investigation Department Sunday visited the spot and also went to the victim's house to speak to her relatives.
According to police, the group of men first attacked the woman and when her husband tried to intervene and resist, he too was beaten up and forced to drink acid.
The woman died on the way to the hospital while her husband was in a critical condition, police said.
The arrested man is a worker in the same brick kiln. Some other people have also been detained for interrogation.
The incident triggered an outcry from the political parties and the civil society.
"The state government calls itself a representative of Ma-Mati-Manush (Mother-Soil-People). But mothers are being assaulted regularly under this dispensation," said Left Front chairman Biman Bose.
"I don't know how many more such cases we have to watch. When will society learn to respect women?" said writer Suchitra Bhattacharya.
There was a nationwide outrage after the 23-year-old young trainee physiotherapist in south Delhi was brutally assaulted and gang-raped Dec 16 by six men in a moving bus before being thrown out of the vehicle. She battled for life -- first in Safdarjung Hospital here and then in a Singapore hospital -- before dying of her injuries Dec 29.