He's charged with murdering Dawn and Antonio Armstrong Sr., while they slept in their southwest Houston home on July 29, 2016. Armstrong was 16-years-old at the time.
Last April, Armstrong was tried for the murders but a mistrial was declared.
The retrial, which was originally supposed to begin Monday, Jan. 6, has now been set for March 27.
RELATED: A.J. Armstrong's lawyers bid to keep text messages out of retrial
A judge is expected to decide whether future jurors will see thousands of text messages extracted from Armstrong's iPhone.
The attorney for Armstrong filed a motion in December asking for Armstrong's phone records to not be allowed into evidence for the retrial.
Armstrong's team argues that, because prosecutors lost Armstrong's iPhone at the end of his first trial, all records extracted from the phone should now be suppressed.
Related: AJ Armstrong speaks out in exclusive interview with ABC13
Defense attorneys now tell ABC13 that 22 pieces of evidence went missing during the first trial, including Armstrong's cell phone. Some of the lost items include shell casings, DNA swabs, and the gun case.
"The prosecution has known for six or seven months that 22 pieces of evidence went missing in a case, thrown out, gone, and they didn't bother to tell us until the Friday before trial," said defense attorney Rick Detoto.
According to defense attorneys, prosecutors knew about the 22 pieces of evidence in May 2019, but only told defense about the exact items on Friday, Jan. 3.
A spokesperson for the D.A.'s office said the bag shouldn't have been mistaken for trash.
"It was with the other evidence," spokesperson John Donnelly explained. "It was presumed to be safe. It was being carried in a bag, back and forth. Sometimes, it's a bag or a box."
ABC13 legal expert Steve Shellist said this is a big deal because a judge could dismiss other evidence tied to what was in the bag. Plus, the jury could learn a bag with 22 pieces of evidence is missing.
On Monday, ABC13 is set to air an exclusive interview with the accused killer. ABC13's Courtney Fischer is the only local journalist to have interviewed Armstrong before both trials.
During the first trial, more than 80,000 pages of phone records were entered into evidence. Prosecutors dissected hours of text messages between Armstrong and his parents that were timestamped from weeks and days leading up to their murders.
The state argued those messages showed Armstrong was angry with his parents because they took him out of private school. They had punished him by taking away his car and video game system due to his grades slipping.
Defense attorneys argued the messages between Armstrong and his parents were normal parent-teen conversations, showing a mother and father who wanted the best for their son.
The above video is from a previous story.
FAMILY SHATTERED: The murder trial of A.J. Armstrong
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