Pablo Escobar AP BOGOTA (Reuters) - One of Colombia's most feared drug cartel assassins walked free on Tuesday after serving 22 years in jail for scores of murders ordered by notorious drug lord Pablo Escobar during the cocaine trafficking heyday of the 1980s, police said.

Jhon Jairo Velasquez, known by his alias 'Popeye', was released early from the high security Combita prison in central Boyaca after completing about three fifths of his sentence and receiving a reduction for studying and good behavior. He left the prison heavily guarded by state-provided protection.

Velasquez, 52, was Escobar's chief hit man during the bloodiest days of the infamous Medellin Cartel, which shipped billions of dollars of cocaine to the United States and Europe.

The prolific assassin, who has admitted to killing hundreds of Escobar's enemies, was on the frontlines of grisly gangland battles for territory and trafficking routes. He was indirectly behind thousands of deaths by killers on Escobar's payroll.

One of Escobar's inner circle, Velasquez was allegedly involved in some of the most famous cartel-related crimes - including the 1989 assassination of presidential candidate Luis Carlos Galan and the bombing of an Avianca commercial flight later that same year that killed all 107 on board.

As Escobar stepped up his battle against the government to avoid extradition to the United States if captured, the cartel waged a bombing campaign across Bogota, Medellin and Cali, with many of the explosive devices planted by Velasquez.

He kidnapped both Andres Pastrana, when the future president was mayor of Bogota, and Francisco Santos, who later became vice president and is a cousin of President Juan Manuel Santos.

Perhaps the most shocking of Velasquez's crimes was the murder of his own girlfriend, who was also Escobar's ex-lover.

The woman, looking for revenge after Escobar forced her to have an unwanted abortion, clandestinely contacted U.S. drug authorities in an effort to become an informant, Velasquez told Semana magazine in an interview last year.

The drug baron ordered Velasquez to kill her, in what the hit man characterized as one of the most painful episodes of his life.

Families of some of the Avianca flight victims have complained that Velasquez has not shared all he knows about the crime and say that his release could mean vital facts never come to light.

During his prison stint, Velasquez provided evidence which helped jail other criminals - including an ex-senator convicted of involvement in Galan's murder.

Ironically, Velasquez's work as a government informant may put him at risk for the same kind of revenge hits that he once carried out on Escobar's behalf.

It is not clear whether the state will provide him with protection.

Like Escobar, who was gunned down by Colombian agents in 1993, Velasquez is a native of Antioquia province, once an epicenter of the narcotics trade.

(Reporting by Helen Murphy and Julia Symmes Cobb; Editing by Tom Hogue)