Premkant Shivji Jha was shot dead by unidentified assailants at Virar in 2012 (Representational)

The CBI on Tuesday announced a Rs 5 lakh reward for information about the 2012 murder of a Right to Information (RTI) activist at Virar in neighbouring Palghar district, an official said.

A Special Task Force or STF of the Central Bureau of Investigation is probing the murder of activist Premkant Shivji Jha.

The STF issued an advertisement in Marathi newspapers Tuesday, announcing a cash reward for anyone providing detailed information about the culprits, the official said.

Identity of the informant will remain confidential, he added.

Mr Jha was shot dead by unidentified assailants at Virar on February 24, 2012 when he was riding a motorbike. The bullets pierced his helmet and entered the head.

Initially, a case of accidental death was registered at the Virar police station, but it was converted into a murder case when an autopsy report revealed the bullet injury.

The probe was transferred to the police's anti-human trafficking cell first, but no headway was made in identifying the culprits.

In October 2014, the CBI took it over on the Bombay High Court's order.

In 2016, the CBI arrested two construction professionals for allegedly hiring contract killers to eliminate Mr Jha as he had sought information about their illegal constructions, the official said.

Mr Jha was part of 'Brashtachar Va Atyachar Virodhi Samiti', an NGO, and had filed several RTI applications and complaints against illegal constructions in the Vasai-Virar area near Mumbai, the official said.

It was also alleged that Mr Jha extorted money or obtained other favours from builders engaged in illegal constructions, he said.