By Megan Hickey

CHICAGO (CBS)– The man charged with stabbing a man to death on the Red Line over the weekend has threatened a stranger in the past.

Court records show it’s the second time this year that Tony Polk has been arrested for threatening to hurt or kill someone.

A woman said Tony Polk raised his hand to her before he was tackled by a security guard. She wants to know why he kept getting out on bond.

Police say a 54-year-old man got into an argument with Polk on a Red Line train on Saturday at the Cermak-Chinatown stop. Polk pulled out a knife and fatally stabbed the man.

Police soon caught up with 40-year-old Polk who was recently paroled from prison for an aggravated robbery conviction.

He was arrested and charged with murder.

Polk’s photo gave a Chicago woman chills because she had a run in with him just last month.

She asked CBS 2 to not reveal her identity.

She was working security in the emergency room at Jackson Park Hospital when Polk came in with a stab wound.

The doctor couldn’t see him right away.

“That’s then when he threatened to hurt me, he stepped in my face he also raised his hand,” the woman said.

Another security officer grabbed Polk before he was able to strike her. He was arrested on the spot.

Court records show he bonded out after posting $750.

“He was able to just walk away,” she said.

Court records show he did the same thing in January. This time, to a man outside a restaurant on the South Side. He told the victim “I will shoot you man, I will stab you too.”

According to the Illinois Department of Corrections, Polk has been convicted of armed or aggravated robbery three times.

His victim from June told CBS 2 she’s horrified to see that this time, Polk appears to have followed through with his threats. But she also said it shouldn’t have come to someone losing their life.

“It is sad that it took to this point that he took someone’s life in order for him to stay behind bars, hopefully he stays behind them,” she said.

It came out in court Wednesday that 54-year-old Troy Johnson was defending another rider on the train when he was stabbed and killed on Saturday.

Polk was denied bond.

As for why he was able to bond out repeatedly in the past since he’s been out on parole, no response from the Cook County State’s Attorney’s Office.

Megan Hickey