Looking back at the late July 2016 night, attorneys focused on the alarm system.
"That night, the alarm was on. The doors and windows were locked to that house. The garage was down," prosecutors said to the jury of 15, made up of nine women and six men. "The murder weapon was still in the house and the killer was not an intruder who came and left. He was in the house the whole time."
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A.J.'s attorneys countered in their opening statements, saying their security experts will show how someone could have gotten into the house without setting off the alarm. They also pointed out what they say is lack of evidence in this case.
"No blood on his clothes anywhere. No gunshot residue on his shirt, on his pants, and no fingerprints," said defense attorney Rick DeToto.
DeToto, as expected, pointed the finger to A.J.'s older half-brother, Josh Armstrong, as the possible killer. It was a bombshell theory they argued in A.J.'s first trial.
"He (Josh) was - and I take no pleasure in saying this - he was absolutely psychotic. Deeply mentally ill and in a rage. And he was never really investigated," DeToto said.
WATCH: See full video of attorneys on both sides presenting opening statements in Houston courtroom
Opening statements in AJ Armstrong second capital murder trial (2022)
This time around, prosecutors were ready to talk about Josh.
"I anticipate they (defense) will ask you to make the leap that he was in the room when he killed his parents," said one of the prosecutors to jurors. "I want you to know that Joshua Armstrong did witness the death of his parents because he was at the scene when they were carted out on stretchers and loaded up in the back of ambulances."
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Both sides introduced the Armstrong family to jurors as the all-American family who had it all: a beautiful home, nice cars, great vacations, kids in an expensive private school. But, the state says that life was crumbling, pointing to text messages between A.J. and his parents that jurors will see over the next few weeks.
SEE MORE: AJ Armstrong trial: Prosecutors reveal text messages sent before parents murdered
"Quite frankly, at the end of spring and into summer, his parents were at wits end with him -- especially the mother, Dawn Armstrong," prosecutors said.
"Did A.J. have problems with his parents?" DeToto countered. "Ladies and gentlemen, how many 16-year-olds don't have problems with their parents?"
One witness took the stand Tuesday -- now-lieutenant J.P. Horelica with Houston police. Horelica was one of the first officers to enter the Armstrong house on Palmetto Street. He described a difficult, bloody scene, where Dawn and Antonio Armstrong laid in their bed, as paramedics worked to try and save Antonio Sr. He later died at the hospital. Dawn was pronounced dead at the house.
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Courtney Fischer's 2020 exclusive interview with AJ Armstrong
Prosecutors showed several photos of what the inside of the home looked like, as well as photos of A.J. and Kaira, A.J.'s younger sister who was 12 at the time, both with their hands bagged, as is the practice when investigators test for gunshot residue.
Horleica's testimony resumes Tuesday morning at 10:30 a.m.
FAMILY SHATTERED: The murder trial of AJ Armstrong
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