A body found in the River Loire is that of a man who went missing after French police raided a music festival last month, local officials say.

The French prime minister has promised “total transparency” in investigating the death of a man following clashes between police and festival-goers in the western city of Nantes, as questions remained over the case.

Investigators confirmed the identity of a 24-year-old man whose body was found in a river more than a month after riot police raided a music festival.

Steve Caniço went missing on the night of 21-22 June after officers moved in to disperse techno music fans attending a free concert in the western city of Nantes as part of France’s national music celebration day.

More than a dozen concertgoers fell into the nearby Loire River during the ensuing clashes, prompting accusations of excessive force by police trying to shut down the party.

An autopsy carried out on Tuesday morning on the badly decomposed body that was found close to the concert site on Monday confirmed it was Caniço, the source said.

Prosecutors said they had opened a manslaughter investigation, and the police have carried out their own internal inquiry.

Footage posted on social media showed scenes of chaos as officers carrying batons and firing teargas moved in on revelers by the river. Local authorities said 14 people were pulled from the water after the clashes.

Caniço’s friends, who said he did not know how to swim, feared he had been swept away in the confusion.

His disappearance drew fierce criticism over the tactics used by police, already under fire for heavy-handed interventions during the weekly gilets jaunes (yellow vest) anti-government protests that erupted last November.

Posters asking “Where’s Steve?” soon appeared around Nantes, and on 20 July hundreds of protesters formed a human chain along the Loire to observe a minute’s silence for the missing man.

Local authorities have also been criticized for allowing the event to go ahead at a riverside venue without sufficient barriers.