(CNN) -- Police in Colombia have arrested four people accused of killing a U.S. Drug Enforcement Administration agent during an attempted robbery.
Colombia's National Police said the four suspects they arrested were part of a criminal network of thieves. Two additional suspects who were allegedly involved in the crime remain on the loose, CNN affiliate Caracol TV reported.
The United States will request extradition of the suspects, but it has not yet done so formally, a law enforcement official said.
Special Agent James "Terry" Watson, assigned to the DEA unit in Cartagena, was on temporary duty in Bogota when he died after being stabbed in a taxi cab last Thursday night, officials said.
Authorities have said they do not believe the attack was connected to his work for the U.S. agency.
"The homicide of the DEA agent was committed by common criminals and was not connected to his work in Colombia," National Police Director Gen. Jose Roberto Leon Riano said, according to Caracol.
U.S. officials praised Colombian authorities Tuesday for their swift investigation.
"The Drug Enforcement Administration is grateful for the outstanding work of the Colombian National Police, the Special Investigative Unit and the Attorney General's Office that led to the swift arrest of these suspects," DEA Administrator Michele M. Leonhart said in a written statement. "We will never forget Special Agent Watson and his sacrifice, as well as all those who have given their lives for the rule of law. We salute the brave and expeditious work of Colombian law enforcement and we look forward to justice being served."
Watson, 42, had been watching the last game of the NBA finals at a Bogota restaurant Thursday night and left in a taxi, a State Department spokesman said last week.
Investigators believe Watson's cab stopped at a traffic light and his assailants jumped out of two other cabs, which pulled up on either side of the vehicle in which he was riding, a law enforcement official said.
According to the official, Watson managed to escape from the cab and was taken to a hospital, where he died.
In Colombia, such attacks are known as "millionaire rides." Authorities said the suspects they arrested were part of a gang known for millionaire ride robberies.
The DEA said Watson was a 13-year veteran of the agency. He had been sent to Afghanistan three times on counternarcotics trafficking assignments and had previously served in the Army and worked for the U.S. Marshals Service.
Attorney General Eric Holder is scheduled to speak at a funeral service for Watson in Louisiana on Wednesday.