Investigators said on Thursday that there was evidence that the soldiers charged over the massacre on May 22 were in the pay of right-wing paramilitary militias out to protect their cocaine smuggling operations.
Mario Iguaran, the Colombian attorney general, told a news conference: "This was a crime. It was not an accident."
The incident, which took place in a rural part of Valle province in western Colombia, had earlier been described by the government as a "friendly fire" accident.
The suspects are accused of gunning down their victims at short range despite the police having shouted, "Don't shoot. We are police. We have children”, investigators told reporters.
German Espejo, an analyst at Bogota thinktank Seguridad & Democracia, said: "The police were fully uniformed and identifiable. The incident happened in daylight and in an area that had a clear line of sight.
"This raises a lot of questions about whether these soldiers were paid by drug dealers to kill this group of police. "There is plenty of evidence that points to it being premeditated."
The government is offering a $400,000 reward to anyone not in the military who can shed light on the incident, in which 28 soldiers were involved.
Thousands are killed and tens of thousands are displaced every year in Colombia's 40-year-old guerrilla war, in which rebels and paramilitaries battle for control of the country's cocaine trade.