Tissue samples taken from Pantani’s body following his death in 2004 have since been destroyed, Gazzetta dello Sport reported on Tuesday.
The autopsy concluded that the cyclist died from a cocaine overdose, but in October two separate investigations were launched to examine whether he could have been the victim of manslaughter.
Destroying medical evidence following an autopsy is the usual procedure under Italian law, the public prosecutor overseeing the case said.
The tissue samples were destroyed in recent months, as Pantani’s family pushed to have the case reopened, Tgcom24 reported.
But some medical evidence still remains, including toxicology tests which have been passed to investigators, Gazzetta dello Sport said.
Pantani died in a hotel room in Rimini, six years after he won the Giro d'Italia-Tour de France double.
The star cyclist had, however, fallen from grace in 1999, when he was thrown out of the Giro d’Italia for having a high red blood cell count. Without a valid test for performance enhancer EPO (erythropoietin), Pantani was excluded for breaking the threshold of red blood cells by one percent.
Speculation has since mounted that the cyclist was forced out of the race to prevent mafia-linked bookmakers suffering huge betting loses.
Pantani’s mother has said that her son was scared of winning the 1999 race.
"He was always telling me, 'Mum, I don't understand. I've always been taught to give my best in bike races. Instead, I'm being told to do the opposite'," Tonina Pantani said in October.
Investigators are now trying to determine whether he could have been the victim of manslaughter, having been forced to drink a deadly liquid in a bid to cover up the events of 1999.