CATONSVILLE, Md. (WJZ) — A Baltimore County police officer shot and killed a man he says pointed a knife at him. WJZ has learned that man was mentally ill.

Derek Valcourt spoke with his heartbroken mother about this shooting.

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“It has devastated our entire family,” said Kathy Shamer.

This Christmas, Shamer prepares to bury her son, 36-year-old Gregory Stegall, who lived with paranoid schizophrenia most of his life. Shamer made sure he took his medication regularly—until early Sunday morning, when he was shot by a Baltimore County police officer who spotted him behind a gas station at Edmondson Avenue and North Bend Road in Catonsville.

“What I think he was probably doing was urinating,” Shamer said.

But police say when the officer told Stegall to step out from behind the gas station, he pulled out a knife. The officer tried to use a Taser on Stegall but police say it didn’t work.

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“It had no effect probably because he lad layers of clothing on because Greg is known to wear multiple sweatshirts and heavy coats,” Shamer said.

Police say the officer had no choice but to open fire. One shot to the chest ended Stegall’s life, hours before he was to celebrate his daughter’s birthday.

“I just couldn’t believe it, that somebody would do that. Why not shoot him in the leg?” Shamer said.

Her family is now trying to make sense of the tragedy and trying not to hold hatred in their hearts as they say goodbye to Stegall.

“In my heart, I’ve been trying to find a way to forgive the police officer that injured him. I hope that he’ll be alright because he’s going to have to live with this or she’s going to have to live with this the rest of their lives,” Shamer said.

Monday, police have identified the officer who shot Stegall as Officer Farrelly, an eight-year veteran of the force. He has been placed on routine administrative leave pending the outcome of the investigation.

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Police say the officer has not been involved in any other shootings.