A mafia traitor was beaten to death with a hammer and then eaten by Serbian gangsters, police believe.
Officers said Milan Jurisic, 37, was killed in Madrid by criminals from the Zemun Clan, a mafia group from Belgrade.
His remains were then ground up with a meat grinder, cooked, and eaten, according to a confession by another Zemun Clan member, Sretko Kalinic, nicknamed "The Butcher".
Later the gang reportedly threw the bones into the River Manzanares in the Spanish capital.
This week, police found bones in the river and the apartment where the killing apparently took place in 2009.
Jurisic is thought to have betrayed his fellow gang members by stealing money from them.
He was on the run after being convicted in his absence of assassinating Serbian prime minister Zoran Djindjic in 2003.
Kalinic confessed to the murder after he was arrested in the Croatian capital of Zagreb in 2010.
Police believe the murder and subsequent cannibalism was led by Luka Bojovic, a Serbian gangster arrested in Valencia last month.
Bojovic was also on the run after being accused of assassinating Djindjic.
Inside Bojovic's apartment in Valencia police found documents backing up Kalinic's account of the killing.
The murder is being investigated by magistrate Fernando Andreu at the National Court in Madrid.