Former mixed martial artist Lumumba Sayers -- who once fought ex-UFC star Derek Brunson inside a cage -- was arrested for murder over the weekend ... after he allegedly shot and killed a man to avenge his son's death.
The Commerce City Police Department says the incident happened at around 5 PM on Saturday during a children's birthday party at a Commerce City, Colo. park.
According to the arrest affidavit, obtained by Denver7, Sayers is accused of walking up to 28-year-old Malcolm Watson and shooting him in the head. The docs state witnesses told cops Sayers may have thought Watson had been a friend of a man he believed to be somehow involved in the 2023 death of Sayers' son.
Records show Sayers is currently in an Adams County jail ... being held behind bars on a $1 million bond. According to 9News, he was booked on charges of first-degree murder and menacing.
Sayers competed in several fight promotions during his professional career -- including Strikeforce, where he lost bouts to Brunson and Anthony Smith.
In retirement, Sayers had been active in his community -- denouncing gun violence, while creating a Heavy Hands Heavy Hearts boxing gym that was designed to keep youth out of trouble.
Sayers is slated to appear before a judge in the case on Thursday.