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NTX scuba death: affidavit states victim not weighted properly, instructor awake for 29 straight hours

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Published  February 13, 2026 4:25pm CST
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FOX 4
Former scuba instructor was sleep-deprived when child drowned

Former scuba instructor was sleep-deprived when child drowned

An affidavit from the arrest of a former North Texas scuba instructor reveals key evidence into why authorities arrested him last Friday for his role in the death of a child student. FOX 4's Lori Brown has more.

The Brief

    • The affidavit regarding the arrest of former scuba instructor William Armstrong reveals key details about his role in the drowning of 12-year-old Dylan Harrison in August 2025.
    • The document states Armstrong was on land without diving gear on when Harrison drowned, and gave contradicting statements to investigators on his location when first responders arrived.
    • It also reveals Harrison was most likely not weighted properly before descending, based on information from the dive computer she was wearing when she drowned.

TERRELL, Texas - An affidavit relating to the arrest of former scuba instructor William Armstrong revealed more details about his role in 12-year-old Dylan Harrison's drowning during a scuba class last fall.

Affidavit reveals troubling details

What we know:

The affidavit states when Able Springs Fire Rescue arrived at the scuba ranch in Terrell, Armstrong was standing on the dock with no gear on. That contradicts what Armstrong initially told investigators, that he stayed in the water looking for Harrison when the first responders arrived.

That report matches a description from a witness at the lake the morning of the accident, stating Armstrong was "bone dry" on land. The affidavit also says no one was in the water searching for Harrison when Able Springs FR arrived.

Dylan Harrison's dive watch was collected as part of the investigation, and it appears to confirm she was not weighted properly. The affidavit states the dive computer's data revealed lines with "sudden up and down motion, believed to be the victim struggling for her last breaths."

Armstrong did not tell authorities of his rank when asked. The affidavit adds that Armstrong, in addition to being Harrison's scuba instructor, was a member of a dive recovery team and a peace officer, who had a duty to act in case of emergency.

He also admitted to authorities that "he had been awake straight for approximately 29 hours, working three jobs." Investigators said the lack of sleep raised concerns about his physical and mental abilities.

Armstrong arrested for role in drowning

The backstory:

William Armstrong was arrested Friday, Feb. 6 and charged with injury to a child for his role in 12-year-old Dylan Harrison's drowning in August 2025. He was released from the Kaufman County jail later that day after posting his $150,000 bond.

He made no comment after he left the jail.

Armstrong was the instructor for 12-year-old Dylan Harrison’s scuba certification class at The Scuba Ranch in Terrell on Aug. 16, 2025.

According to witness affidavits obtained by the family's attorney, there were eight students, an instructor, and a dive master in the class. 

During the class, Dylan went missing. Her body was later found away from the platform at a depth of about 45 feet, according to the family's attorney.

Armstrong resigned from his position with the Collin County Sheriff’s Office in October. He was also "permanently suspended" from teaching classes at The Scuba Ranch.

Records obtained by FOX 4 showed that on the day before Harrison’s death, Armstrong worked a full day as a deputy, and then a full overnight security shift at an investment firm.

Sympathy in court unlikely

What they're saying:

Appellate attorney Chad Ruback, who is not associated with the case, told FOX 4's Lori Brown that Armstrong is unlikely to receive sympathy in court based on what he told investigators.

"It's as if someone says, well, they shouldn't be culpable. They shouldn't be guilty of committing all sorts of crimes because they were drunk or because they were strung out on drugs. That doesn't help their case. It hurts it," Ruback said. "I think a lot of things about this case will bother a jury. I think Mr. Armstrong's actions, again and again and again, seem to be in such a way that if it were in front of a jury, the jury wouldn't just convict him in my mind, they would be furious at him."

Last week, the parents of 12-year-old Dylan Harrison filed a lawsuit against two major scuba agencies, alleging that systemic safety failures led to her drowning during a certification class on Aug. 16, 2025.

The lawsuit alleges systemic safety failures in the self-regulated industry led to Dylan Harrison's death at The Scuba Ranch in Terrell. 

The 40-page suit details multiple failures that the lawsuit claims are the result of the scuba diving industry turning a blind eye to safety failures for years. 

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