HOUSTON, Texas (KTRK) -- From the opening arguments on Monday morning, it was clear the details of this case are heart wrenching. Prosecutors described a methodical execution of Katie and Stephen Stay, and four of their children.
Only daughter Cassidy Stay, then 15, survived a bullet wound to the head.
"She (Cassidy) can hear the shooting continue down the line. Emily. Bryan. And then another shot and Zachary stops crying," said prosecutor Samantha Knecht. "They recovered 13 casings from the Stay living room. Thirteen. And that every one of those casings comes back to that 9mm that was found with the defendant when he was in custody."
The first piece of evidence was Cassidy's 911 call.
She tells operators her whole family is shot. She needs help. And when asked who shot her family, she tells them her Uncle Ronnie.
As it was played, Ron Haskell sat still in his chair, his head down. He doesn't deny what happened. His attorneys claim he was insane.
"He's sedated and he's an individual that's been treated for a severe mental illness," said defense attorney Douglas Durham. "Texas has an insanity statute and if this isn't a case where the evidence, a preponderance of the evidence, is going to show severe mental illness and he couldn't distinguish right from wrong, I don't know what case there is."
It is a tough defense. They have to prove he was insane and didn't understand the consequences of his actions. Prosecutors will try to convince the jury it's not so and that he killed the Stays for helping his ex-wife leave him.
"The credible evidence will show you that this was not a case about someone who was insane," Knecht told the jury. "That this rather was a plan that was created in anger and fueled by vengeance."
Prosecutors argued in opening statements that Haskell killed the family as retribution for helping his ex-wife, Melanie, separate from him. Katie Stay was Melanie's sister.
The first witness to take the stand was a Harris County Pct. 4 deputy constable who was the first to respond. Sgt. Beck testified the scene was surreal and that after he helped Cassidy, he checked all six victims for a pulse.
Prosecutors played an audio recording from a device Beck was wearing. It revealed a panicked scene while first responders worked calmly to assess the scope of the crime and treat Rebecca Stay, who at the time still had a pulse and was breathing.
Jurors sat motionless, their attention rapt, their faces drawn from the emotional audio.
Haskell faces the death penalty if convicted.
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STAY FAMILY TRAGEDY