Their youngest son, Antonio Armstrong Jr., who goes by A.J., was charged with killing them. He was 16 years old at the time.
Now, A.J. Armstrong is a 21-year-old father himself, gearing up for his double capital murder retrial set to start in January 2022.
For the past two years, since his first trial ended in a mistrial, A.J. Armstrong has been living with his grandmother while out on bond. He's been helping raise his newborn son, Hendrix Antonio Armstrong, along with girlfriend Kate Ober, who was a witness during his first trial in April 2019.
"I've seen him in some very dark, difficult times over the years," said A.J. Armstrong's attorney, Rick DeToto. "I've seen him go through a lot of stress and now I see a rejuvenation, a happiness, a goal."
READ ALSO: 'I didn't do it:' Accused killer A.J. Armstrong tells his story
That goal is to instill the same values in his son that A.J. Armstrong's parents instilled in him, DeToto said.
But, to prosecutors, A.J. Armstrong murdered his parents because they were hard on him over slipping grades, breaking curfew and smoking marijuana - tension revealed over text messages in his first trial.
His team dropped their own bombshell during that first trial: arguing the then-teen's older half-brother, Josh Armstrong, Dawn's biological son, could be the real killer because he was mentally unstable at the time and allegedly heard voices in his head.
READ MORE: AJ Armstrong's brother told doctors he witnessed parents' murders
DeToto did not discuss specifics about strategy in the retrial, but said they have more evidence about the "alternative perpetrator" theory, which was presented Friday in the pre-trial hearing and allowed to go forward.
"Some evidence we found since the last trial where the person indicates they were present when the parents were murdered, so it's a really important, very important, hearing for us," DeToto said.
FAMILY SHATTERED: The murder trial of A.J. Armstrong
Also discussed in the pre-trial hearing were the 22 pieces of evidence lost after trial one.
Those items include A.J. Armstrong's cell phone, shell casings, DNA swabs along with other items. The judge denied a defense request to hear about the lost evidence.
READ MORE: Evidence bag missing from AJ Armstrong double murder trial
The defense also argued text messages from his phone should not be allowed in retrial because the phone is gone. The judge has not ruled on that yet.
In 2020, a spokesperson with the Harris County District Attorney's Office told Eyewitness News the lost evidence was in a bag mistaken for trash.
A.J. Armstrong's retrial is currently set to begin January 4, 2022. He will be 22 by then.
"He's gone from a typical, immature 16-year-old boy to a ... he's become a man," DeToto said.
WATCH: Full uncut interview of AJ Armstrong
While this case has dragged on, partially due to the COVID-19 pandemic pushing back recent court dates, the defense believes that could be good for A.J. Armstrong.
"Memories fade, police officers get in trouble, witnesses get in trouble, so just a general statement for what I do, it's better for us. Not always, but in general, it is," said DeToto.
ABC13 reached out to prosecutors for comment.
They declined, but sent ABC13 part of a transcript from a pre-trial hearing from back in February in which the judge warned both sides to "use caution" when moving forward in speaking with the media.
Due to how much publicity has surrounded the A.J. Armstrong case, the judge did not go so far as to issue a gag order, citing the first amendment.
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