Published: May 13, 2014 11:31 AM EDT

TAMPA, Fla. (AP) - The ex-husband of a woman accused of killing her two teenagers is on the witness stand in her Tampa, Florida, trial.
    
Defense attorneys on Tuesday called Parker Schenecker as a witness.
    
He and Julie Schenecker were married in January of 2011, when police say she shot and killed their 16-year-old daughter Calyx and their 13-year-old son Beau in the family's home.
    
The couple divorced after the deaths.
    
Parker Schenecker told the jury Tuesday that his wife's depression and mental illness was a constant "drum beat" in their relationship.
    
Schenecker is charged with two counts of first-degree murder. The state is not seeking the death penalty and contends Schenecker knew right from wrong when she bought a gun and shot her children.

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