(Updates with 4th arrest, U.S. extradition request)

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Colombian authorities on Tuesday arrested four suspects in last week's murder of a U.S. Drug Enforcement Administration agent, police sources told Efe.

One of those arrested appears to be the driver of the taxi in which James "Terry" Watson was traveling through an exclusive sector of northern Bogota when two men entered the vehicle allegedly to rob him, but then stabbed him several times, killing him.

Police are still looking for two other suspects.

Authorities suspect that those responsible for Watson's death belong to a gang of robbers of taxis who perpetrate so-called "millionaire outings" during which they rob the rider of his belongings and force him to withdraw money from his bank account at various ATMs.

The initial investigation into those responsible for the murder indicate that they could belong to a Bogota gang called Los Canarios.

Colombia's top cop, Gen. Jose Roberto Leon Riaño, said at a press conference that "the murder of the DEA agent (occurred as a result of) common crime and was not due to his carrying out the tasks he was pursuing in Colombia."

The police director also said that a U.S. federal court requested the extradition of the four suspects.

Watson, who recently married a Colombian woman, worked from a DEA office in Cartagena and was in Bogota on business last Thursday when he gathered with personnel from other embassies to watch Game 7 of the NBA Final on television. EFE