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ARAPAHOE COUNTY, Colo. — A mother and her son have been convicted in the killing of a witness in a marijuana shop robbery case in Denver in 2016.

Terance Black and Tina Black were convicted of first-degree murder in the death of David Henderson last week after a joint trial that began on Jan. 22.

They were sentenced to life in prison on Thursday in Arapahoe County District Court.

David Henderson

Prosecutors said the Blacks learned Henderson was cooperating with law enforcement because the court mistakenly sent out unredacted arrest affidavits to people involved in the case. Prosecutors said the Blacks then arranged to kill Henderson.

“In some ways, this was a perfect storm of different events that took place. There were a number of affidavits on a number of cases that were sent out, but they were sent to a number of people who would never dream of trying to murder the witnesses against them. It just happened to reach the group willing to do it in this case,” said 18th Judicial District Attorney George Brauchler.

Documents in the case were sealed because other witnesses and a cooperating defendant were in fear for their lives, leading to “intense” security measures, the 18th Judicial District Attorney’s Office said.

RELATED: Terance Black affidavit

The robbery case in which Henderson was a witness occurred at Cure Dispensary at 6200 E. Yale Ave. in southeast Denver on Aug. 14, 2016.

Henderson was found fatally shot on Oct. 12, 2016, outside his home at 425 S. Galena St. in Denver.

Brauchler applauded Henderson doing the right thing despite threats against his life.

“[The Blacks] initially made some threats, came to him, there was a gun put in his face, threatened if he would continue to cooperate, it would result in the loss of his life. That had a profound effect on him, but not so much that it overwhelmed his sense of duty and righteousness. He moved forward and died as a result,” said Brauchler.

Terance Black and Tina Black were convicted of first-degree murder after deliberation and conspiracy to commit first-degree murder after deliberation.

Tina Black was also found guilty of conspiracy to commit burglary and conspiracy to commit aggravated robbery.

Henderson’s loved ones were at the courthouse.

“It’s important I go public and talk about it, because I want people to know they can’t get away with this. You should never threaten a witness and you should never murder a witness,” said Karen Henderson-Atkins, Henderson’s sister.