The mass shooting after the Nuggets' championship win in Denver on Tuesday morning appeared to be sparked by a drug deal gone wrong ... this according to cops.
Denver chief of police Ron Thomas made the revelation on Tuesday afternoon ... explaining that they discovered cash, firearms and what appeared to be fentanyl at the scene -- all signs that point toward a botched drug deal.
Two people, Thomas said, are in police custody -- though their exact involvement remains unclear.
Of the 10 people that sustained gunshot wounds, authorities said they believe five or six were innocent bystanders. All 10, thankfully, are now in "fair condition," according to officials ... though five still remain in the hospital.
The gunshots initially broke out about a mile from Ball Arena at around 12:30 AM ... roughly three and a half hours after Denver beat Miami to win the NBA title in Game 5.
Officials praised the actions of responding officers -- releasing video from the scene that showed cops running toward the gunshots in an effort to keep people safe.
An investigation into it all, officials added, remains ongoing.
As for the championship parade that's planned for Thursday -- officials told reporters Tuesday they are confident they'll be able to keep peace and prevent similar incidents from happening at the celebration.