Additional Superintendent of Police, South 24 Parganas (West) Rabindranath Abharu said four persons have been arrested in connection with the incident.
However, the prime accused who was in a relationship with the woman is absconding, he said.
Abharu said the woman, who had been deserted by her husband and lived with her mother at Akra, had been called from home by Shafiq, the person with whom she was said to be in a relationship, on July 31 evening.
The woman was then offered a drink and she lost consciousness after consuming it.
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The five then allegedly gangraped her and threw her out of the vehicle at around 11 PM at Akra, he said, adding she was spotted by locals, who informed her family.
The woman was rushed to a hospital in Kolkata in a critical state.
Following a named FIR lodged by her mother, the police arrested two of the attackers late that night and seized the autorickshaw.
The two arrested on July 31 night were produced in court and remanded in police custody for a week.
"I have asked for a report. We condemn such incident. Strong action will be taken against unruly auto drivers," State Transport Minister Madan Mitra said.