Italian prosecutors are to launch an inquiry into claims that Marco Pantani, one of the most charismatic and controversial figures in modern cycling, was murdered.

The last rider to win the Tour de France and the Giro d’Italia in the same year, 1998, Pantani was the supreme climber of his day. Known as Il Pirata (The Pirate) because of his beard and penchant for bandanas and earrings, he died 10 years ago after a massive ingestion of cocaine.

It is widely accepted that before his death he was taking growing quantities of the drug for recreational purposes. But it emerged at the end of last week that Pantani’s relatives had presented new evidence to prosecutors in Rimini, suggesting he was forced to drink a potion containing a huge volume of cocaine.

Two local drug peddlers confessed to having supplied the rider with 20 grammes of cocaine five days before he was found dead in a Rimini hotel suite. They bargained a plea. A third man – the head of a hostess agency – was tried on a charge of contributing towards Pantani’s death and was acquitted on appeal.

The shaven-headed rider entered a downward spiral in 1999 after he was thrown out of the 1999 Giro following the discovery of high levels of haematocrit in his blood. The suspicion was that he had been using endurance-enhancing erythropoiesis-stimulating agents, which boost the volume of haematocrit.

But doubts about whether Pantani had committed suicide, which soon became the accepted view, were expressed soon after his death. At his funeral, his mother Tonina shouted out “They killed him!”. And in 2007 a French journalist, Philippe Brunel, published a book, Vie et mort de Marco Pantani, which criticised the conduct of the investigation.

According to Italian media reports the dossier submitted to the prosecutors highlights several elements that were either missed by police or, in the view of the family’s lawyers, given insufficient weight. Investigators at the time concluded that no one had visited Pantani’s room in the hours leading up to his death.

But an independent inquiry was said to have found that there was a second entrance to his hotel, which was not monitored by CCTV. Marks found on the rider’s body were allegedly more consistent with a scuffle than with injuries he had inflicted on himself falling semi-conscious to the floor. And, the family reportedly maintains, the 20 grammes of cocaine would not have been enough to kill him, especially since some of it was found scattered across the floor of his suite.

Rimini’s chief prosecutor, Paolo Giovagnoli, confirmed that the file on Pantani’s death had been reopened. But he described it as an “obligatory move”.