Police on Friday said they suspect the victim to be a man in his 40s with previous convictions for drugs, Rome daily Il Messaggero reported.
However, they are still awaiting the results of DNA tests to confirm the man's identity.
The leg, which was discovered by a fisherman on Tuesday near the Tiber river in the north of the capital, is severed below the knee and sports various tattoos including the words “a good day to die” and a football slogan supporting one of Rome's teams, Lazio.
According to an autopsy carried out at the Gemelli hospital in Rome, the man was killed and probably cut into pieces using an electric saw. The leg was thought to have been in the water for less than two days.
The tattoos have been key to the investigation into the man's identity.
Since the grisly discovery, police have been interviewing tattoo artists in the Lazio area as well as those who have reported people missing, particularly fanatical football fans known as ultràs in Italy.
Police are not ruling out the possibility other body parts could be found.
On Thursday afternoon investigators dredged the area of the river Tiber where the limb was discovered.