A convicted armed robber who was paroled from prison four months ago has been charged with murder in the fatal stabbing of a man aboard a Red Line train in Chinatown last weekend.

Tony Polk, 40, was charged with first-degree murder and is expected to appear in bond court Wednesday. He was arrested at his home in South Shore Monday morning.

Shortly before 3 p.m. Saturday, 54-year-old Troy Johnson was on a southbound Red Line train near the Cermak-Chinatown station when he got into an argument with another man on the train, police previously said. The man took out a knife and stabbed Johnson several times in the chest before getting off the train and running away. Johnson was declared dead at the scene.

A day later, police released surveillance photos of two people — a man and a woman — who were wanted for questioning in the murder.

A police source with knowledge of the investigation said the woman saw her photo circulated in the media and voluntarily went to the police “to clear her name.” Speaking with investigators, she told them that Polk was the person who stabbed Johnson, the source said. The woman is classified as a witness and not a suspect.

The woman told police that, after the stabbing, Polk gave her the knife. She took another Red Line train north to the Fullerton station in Lincoln Park and hid the knife in a nearby flower pot, the source said. Security footage from DePaul University captured her putting the knife there. Detectives have since recovered the weapon, which was still where she put it.

Other security cameras recorded Polk — who himself was cut during the stabbing — taking off his jean vest and using it to clean the knife, the source said. He also cut off a portion of the vest and used it as a bandage for his wound.

Court records show that Polk has been arrested dozens of times since 1997 on charges that include drug possession, aggravated assault, unlawful use of a weapon, battery, robbery and domestic battery.

Prior to being taken into custody Monday morning, he’d already been arrested twice in 2019. In January, he was arrested on retail theft charges in the South Loop. In June, he was charged with assault after being arrested in South Shore.

Prison records show that Polk has four previous felony convictions — three of which were for robbery.

In December 2014, Polk was sentenced to six years in prison after he pleaded guilty to an armed robbery in the 6800 block of South Jeffrey. He was given credit for the 388 days he spent at the Cook County Jail and he was released from prison on parole on March 7, 2019, prison records show.

Polk is no stranger to high-profile criminal cases in Chicago.

In 2016, he testified in the criminal trial of Donnell Flora, who was convicted of giving a gun to his niece, who later shot and killed 14-year-old Endia Martin.

Polk said that, while he and Flora were held in the Cook County Jail in 2014, Flora admitted to him that he gave his niece the gun, with Flora saying of the teen: “That b---- got what she deserved.”