Luka Bojovic, one of the suspects wanted for the assassination of Serbian Prime Minister Zoran Djindjic in 2003, was arrested in Spain.
Police apprehended Bojovic, a Serbian national, in a restaurant in Valencia on Thursday. He is believed to be the head of the Zemun clan, a notorious Belgrade-based division of the Serbian Mafia.
Bojovic is also wanted for more than 20 murders in Serbia, Holland and Spain, according to CNN.
Djindjic was murdered in Belgrade on March 12, 2003. He was killed by a sniper as he was entering his office in the capital.
Djindjic's reformist policies -- including a crackdown on organized crime and and his decision to hand over Slobodan Milosevic to the International Criminal Tribunal for the Former Yugoslavia -- made him an unpopular figure to some. The Zemun clan had tried to assassinate the prime minister before, and in February 2003 a member of the gang tried to force Djindjic's car off a bridge.
The sniper was Zvezdan Jovanovic, a Zemun member and former Red Beret Special Operations solider under Milosevic. He was sentenced to 40 years in prison.
The arrest of Bojovic, a co-conspirator, comes just days after two other convicted Zemun clansmen tried to escape from a high-security prison in Belgrade.
Sretko Kalinic and Zeljko Milovanovic cut through the bars of their cells and jumped out of a window, but were caught by police outside the prison yard, according to Radio Free Europe.
Kalinic was serving a 30-year sentence for his involvement in the Djindjic assassination, while Milovanovic was serving a 40-year sentence for the murder of a journalist in Croatia.
Five prison guards have been detained on suspicion of aiding the prisoners' escape.