Amnesty India on Tuesday demanded that authorities in Tamil Nadu initiate an investigation to find environmental activist S Mugilan, who has been missing since February 15.

Amnesty India said Mugilan disappeared the day he held a press conference in Chennai where he accused senior Tamil Nadu police officials of colluding with the Sterlite plant to “orchestrate violence in Thoothukudi during the protests in May 2018” against the copper smelter plant. He had named Indian Police Service officers Shailesh Kumar Yadav and Kapil Kumar Saratkar.

“Mugilan telephoned a colleague before boarding a train on 15 February,” Amnesty India tweeted. Mugilan told the colleague that he feared being targeted by police asked the colleague to file a complaint if he did not reach Madurai by February 16. Amnesty India said the activist’s family and colleagues have not heard from him since February 15.

“The Tamil Nadu government must ensure that dissenting voices in the state are protected, and that human rights defenders, activists, journalists and lawyers can work without fear,” Amnesty India said.

National Secretary of the Human Rights Defenders’ Alert – India, Henri Tiphagne, told Amnesty India that the Tamil Nadu police have not been cooperative. “That is why we had to file a habeas corpus petition in the [Madras] High Court [on Monday],” he said, according to The News Minute. “This is another example of how dangerous it has become for activists in the state.”

The Madras High Court has issued notices to the Chennai commissioner of police and the superintendents of police of Kanchipuram and Villupuram districts with regard to the habeas corpus petition.

Also read: TN activist goes missing after accusing police of orchestrating last year’s Thoothukudi violence