A suspected serial killer who identifies himself as 'Hercules' has been targeting and killing alleged rapists in Bangladesh, The Statesman reported on Sunday.

Over the last two weeks, police have recovered three bodies with similar notes hanging around their necks from the Jhalakathi and Dhaka districts, the daily reported.

A madressah student in Pirojpur district's Bhandaria area reported being gang raped by two men on January 14 when she was on the way to her grandparents' house, The Daily Star reported.

Her father registered a case on Jan 17 against two male suspects identified as Rakib and Sajal.

In a separate incident on Jan 7, an 18-year-old garment factory worker was found dead in her house in Ashulia, on the outskirts of Dhaka, hours after she had filed a rape case against a man identified as Ripon and three other co-workers, The Daily Star reported.

On Feb 1, police recovered the body of suspect Rakib, 20, from the Rajapur sub-district of Jhalakathi. A note in Bengali ─ undersigned Hercules ─ hanging around the suspect's neck read: "I am Rakib. I am the rapist of a madressah girl ... of Bhandaria. This is the consequence of a rapist. Be wary rapists."

Rakib had sustained bullet wounds to the head, Rajapur police station officer-in-charge M Jahidul Islam told The Daily Star. He confirmed that the law student was shot early in the morning. The body was sent for an autopsy, he added.

On Jan 24, the body of Sajal ─ who was also shot dead ─ was discovered with a similar note around his neck in Kathalia sub-district of Jhalakathi, while on Jan 17, police had recovered the body of Ripon from the Savar area near Ashulia with a note around his neck.

Jahidul Islam said that police are investigating the murders but so far remain clueless about the identity of Hercules.

Rights group Ain-o-Salish Executive Director Sheepa Hafiza raised concern over the murders, saying that killing people "extra judicially" and leaving such a note was unacceptable.

She advised proceeding with caution, The Daily Star reported. "We have to look very carefully into why such incidents are taking place," she said.