A witness trained in first aid said she ran toward the injured couple and "started plugging holes." View Full Caption DNAinfo/Patty Wetli

RAVENSWOOD — A 17-year-old boy has been charged in the double stabbing of a 20-year-old man and 18-year-old woman that left the older man in critical condition near the Western Brown Line stop Thursday afternoon.

The boy, whose name was not released due to his age, was charged with two felony counts of aggravated battery with a deadly weapon, said Officer Jose Estrada, a Chicago Police spokesman.

He had an altercation with the two victims before stabbing them, Estrada said. He was arrested Thursday around 11:50 p.m.

Patty Wetli details the incident:

One witness, Danielle, who withheld her last name, was working at the first Thursday night Lincoln Square Farmers Market of the season when she said she heard people running down the "L" stairs yelling, "Help us!"

Danielle, who is trained in first aid, said she saw the blood, grabbed paper towels then ran toward the injured couple and "started plugging holes."

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