Attorneys use alarm records to suggest killer came from inside the house in AJ Armstrong trial

HOUSTON, Texas (KTRK) -- Understanding the Armstrong family's ADT home security system is an essential part of A.J. Armstrong's capital murder trial. But, the records are tedious, monotonous, and complex-a lot for the six men and six women on this jury to process.

For more than eight hours, Wednesday into Thursday, Harris County Assistant District Attorney Ryan Trask tried to walk jurors through how the alarm system records activity, focusing on the night into the morning of the murders.

The video above is from a previous report on day 3 of the trial.

Investigators say Antonio Sr. and Dawn Armstrong were murdered between 1 a.m. and 2 a.m. on July 29, 2016. Police say Armstrong killed his mother first, shooting her twice in the head, then shot his father.

Armstrong has long maintained he's not the killer, telling police he heard shots come from his parents' bedroom on the second floor as he was walking downstairs to get medicine and saw a masked man run from the house.

Prosecutors played Armstrong's 12-minute 911 call for the jury, in which the then 16-year-old can be heard turning off the house alarm as he unlocked the door and let officers into the Armstrong home on Palmetto Street.

The alarm was set, the doors and windows were locked, and that's why the killer had to come from inside the house - that's what prosecutors have said for three trials now.

But, defense attorneys argue the system and the records can't be trusted.

Before digging into the alarm records from the night and morning of the murders, Trask spent hours explaining to the jury how the system worked.

SEE ALSO: 19,000 pages of text messages dissected in A.J. Armstrong third's capital murder trial

Alarm.com is the company that manages the alarm records, and data delivered to their servers via a cloud system, while ADT is a company within Alarm.com that provides the hardware-think: the physical alarm panel and motion sensors. Experts from each company testified Thursday.

According to evidence introduced by prosecutors, the alarm records from the night/ morning the Armstrong were murdered are as follows:

JULY 28, 2016

9:52 p.m. - Armstrong panel was armed "stay"

9:57 p.m. - Living room sensor went "idle"

10:39 p.m. - Upstairs sensor went "idle"

JULY 29, 2016

1:09 a.m. - Upstairs motion sensor activated

1:25 a.m. - Living room motion sensor activated

1:56 a.m. - Alarm disabled by key fob

1:57 a.m. - Front/garage door open/(and) close

Jason DaCosta, a vice president for Alarm.com, testified that on the night and morning of the murders, the above records are accurate.

A.J. Armstrong's bedroom was on the third floor, while his parents' bedroom was on the second floor, which is relevant to understanding these records, Trask said.

Furthermore, he told jurors the log proves an unknown killer could not have entered the house because it would have set off the alarm.

But, defense attorney Chris Collings argued there are "errors" throughout the hundreds of pages of records, meaning the log from the night in question could be wrong.

"There are likely a small percentage of errors that occur," DaCosta agreed during cross-examination.

SEE ALSO: From crime scene to courtroom: Courtney Fischer takes you inside the AJ Armstrong case

He explained those "errors" to be similar to a "dropped cell phone call," accounting for "less than one percent" of the 9,000 events of alarm activity.

For example: There are times in which the records show a door is opened, followed by another record of the same door opening, which, is impossible. DaCosta explained while the record of the door "closing" was not relayed to their cloud system, it doesn't mean it didn't happen.

"You can't read alarm records by just a couple lines," DaCosta testified. "You have to understand it in the context of all the activity."

Aside from understanding the records, prosecutors and defense attorneys also tackled the motion sensors, window sensors, and keypad panels.

Hour after hour of trying to explain extremely technical alarm systems and records left several jurors bleary, some struggling to stay awake. Then, Trask brought it all back to the Armstrong text messages the jury saw one day earlier.

On Wednesday, the state introduced a text thread between Armstrong and then-girlfriend, Kate, in which Kate asked Armstrong to come pick her up from a party after midnight. Armstrong agreed to come, but the next morning, he texted his mother that he didn't leave the house after Dawn expressed anger about him leaving.

Trask put those texts back on the courtroom TV for the jury, in the context of trying to explain the accuracy of the Armstrongs' alarm system. He then showed the alarm records from that same evening, which show someone exited the Armstrong home around the same time A.J. texted Kate saying he was coming.

"I will show you where you went wrong," Dawn texted her son the following morning. "The alarm doesn't lie. You lie."

For updates on the A.J. Armstrong trial, follow Courtney Fischer on Facebook, Twitter and Instagram.