Sincere Williams, 18, tried to rob the pharmacy in the Wicker Park neighborhood early Sunday before he grabbed Olga Marie Calderon, 32, a mother of two, by the neck as she was stocking shelves, police said.
He then stabbed her several times as she tried to push him away.
“In this case, whatever set him off — whether it was the slight pushback or whatever it was — it just immediately turned from a robbery that quickly to a brutal killing,” Police Cmdr. Eric Winstrom said.
Sincere Williams, 18, was charged with fatally stabbing a Walgreens employee on Sunday. (Chicago police)
Investigators reviewed security-camera footage to track Williams back to the apartment complex where he lives, Winstrom said, adding that the suspect didn’t take anything from the store.
Detectives found a knife and clothing Williams allegedly discarded in a nearby yard, the commander added.
Williams was said to have committed two previous robberies last Wednesday, one at the same Walgreens store and another at a Walgreens in a different neighborhood, authorities said.
The suspect was charged with first-degree murder and has a court hearing scheduled for Wednesday. It wasn’t immediately known if he has legal representation.
It wasn't immediately known if the suspect and Calderon had any previous interactions, authorities said.
“This is an unbelievably tragic incident,” Chicao police Chief of Detectives Brendan Deenihan said Tuesday, according to the Chicago Sun-Times. “To just be at a Walgreens, working for your family, and to have somebody, an offender, come in and commit a heinous act like this and stabbing the victim to death.”
The bloody crime came amid a violent Labor Day weekend in the city that saw 10 murders, 38 shootings, and 51 shooting victims between 6 p.m. Friday and 11:59 p.m. Monday, a Chicago police spokesperson told Fox News.
On Monday, an 8-year-old girl was fatally shot and three others were wounded as they traveled in a Subaru SUV on the city's South Side when a vehicle directly behind them opened fire at a stoplight, in what police said was a "targeted attack."
The child was taken to a local area hospital with a gunshot wound to the back, where she was pronounced dead around 6:30 p.m., police said
“I stand before you, saddened and angered that another child has lost their life in senseless gun violence in the city of Chicago,” Brian McDermott, chief of operations for the Chicago Police Department, told reporters Monday night.
"We're out there every single day doing our best to protect the citizens of the city and that's what we're going to continue to do," McDermott continued.
Fox News’ Stephanie Pagones and The Associated Press contributed to this report