A Glen Arm woman accused of shooting her estranged husband to death is mentally ill, her attorney told a jury this morning, going so far as to compare Mary C. Koontz, 60, to John Hinckley Jr. — the man who shot former President Ronald Reagan — during opening arguments.

Koontz, whose trial began today, faces seven charges, including first-degree murder and first-degree assault. The prosecution intends to seek a sentence of life in prison without parole.

Ronald G. Koontz, a former teacher and wrestling coach at Towson High School who later became an administrator in the Baltimore County school system, was killed June 19, 2009, three days before father's day.

Prosecutor Robin S. Coffin told the jury that Mary Koontz flew from Florida where she was living, woke up before 6 a.m. in the Towson hotel where she was staying, took the gun and ammunition she had earlier purchased and went to Glen Arm. There, Koontz parked at an adjoining property and snuck through the woods. Once at the house, Coffin said, Koontz removed her shoes, snuck into the house and shot her estranged husband in the bed they once shared.

Coffin said that Koontz also shot at her daughter, but missed.

Defense attorney Richard M. Karceski told the jury that Koontz is mentally ill and therefore not criminally responsible. Karceski invoked John Hinckley Jr., saying that Hinckley, like Koontz, was found to have a mental disorder; and that both shootings were part of a love story.

"This is what we have here, a love story," he said.

The illness, Karceski said, prevented Koontz from knowing the consequences of her actions. When a person suffers such an illness, he said, "you're like a pedal bike with a flat tire."

Coffin conceded that Koontz is mentally ill but said she is still responsible for the crimes.

Testimony in the case is expected to begin this afternoon.