Armstrong is a free man after Austin decided not to move forward with the case against him.
Armstrong first appeared before the Sunflower County Justice Court on March 11 after he was accused nearly a month after the murder.
Armstrong's name had come up a few times in the ongoing investigation and Judge Gwendolyn Pernell ruled there was enough evidence to charge him at his initial appearance.
He was being held at the Sunflower County Jail in Indianola on a $100,000 bond.
Sunflower County Sheriff James Haywood said that investigation would continue with extreme dedication from his department.
"Just because the prosecutor felt the case wasn't strong enough doesn't mean it can't be re-presented to the grand jury," said Haywood.
"We are not going to let this rest. Our investigation is ongoing and our work will not stop," said Haywood.
Haywood added that his department is now looking for more leads in the case.
The victim, Burnett, was found dead in his house by authorities on Valentine's Day after his sister called in and said she discovered his body.
The unknown suspect allegedly ransacked Burnett's house, took jewelry and shot him twice in the back of the head.
Haywood is suspicious of other suspects being involved and he believes the incident is drug related.
The guilty party may also face charges related to theft.
"I won't feel good until we get to the bottom of all of this," said Haywood in a previous Bolivar Commercial story. "It will require tedious investigation to find out if more people are involved.
"We have a family here that is waiting for justice."
The murder happened at 170 Hunter Ave. in the new edition subdivision considered to be county land, outside of Drew city limits.
Haywood asked citizens to remain mindful that some crimes take longer than others to solve, but his crew is doing everything it can.
"It's unfortunate, but sometimes things don't get solved overnight. We're still asking for the community's help so we can get all the details.
"Anyone with information, please call the Sunflower County Sheriff's Department at 662-887-2121."
The case marks the second murder in the same neighborhood within the last year.