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Sincere Williams, 18, has been charged with one felony count of first-degree murder, police said.
Police say Williams walked into the store at 1372 N. Milwaukee just after 9:30 a.m. with the intention of robbing the place, police said. Instead, investigators say the crime escalated to murder.
"He approached the victim, Olga Calderon, who was just stocking shelves at Walgreens, grabbed her around the neck," Area 5 Commander Eric Winstrom said. "It appears that she tried to push away from Williams, and he began stabbing her multiple times, causing her death."
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Police said Olga Marie Calderon's co-workers found her dead in a pool of blood inside the store just before 10 a.m.
"I don't really know what to think," Walgreens employee Jennifer Montanez said. "Very numb. It's hard to process, even if it's not someone that you particularly know."
Police said surveillance video and a trail of blood, clothes, and weapons helped investigators track the alleged murderer from the Walgreens to his Old Town apartment.
"Williams discarded a knife and clothing in a nearby yard, which detectives recovered," Winstrom said. "We were able to determine that Williams entered an apartment complex in the 1400-block of North Sedgwick in the 18th District. With the assistance of 18th District tactical personnel, we were able to arrest Sincere at his apartment without incident."
Police don't believe Calderon was targeted for any reason. They said she was just a young working mother trying to make a living who never made it home her family.
"Extremely tragic to have a woman go to work and not come home to her child," said Chicago Police Chief of Detectives Brendan Deenihan.
Crisis responder Andrew Holmes said the woman who was killed is the mother of a 3-year-old boy and an 11-year-old girl. Her family is struggling to come to grips with the loss.
"Her daughter is taking it really hard," Holmes said. "The younger baby doesn't understand yet what's actually happened, but the daughter, she knows."
"It makes me really sad we are in a place in society where we are worried about going home, going to work and we don't know if we're going to come back, we don't know if we're going to upset someone. We just don't know," Montanez said.
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Flowers lie outside the doors of the still-shuttered Walgreens where Calderon was working the register Sunday.
Regular customer Robert Szabla said Calderon was joking around with him about 10 minutes before she was killed when he went there to make a purchase.
"She said, 'Oh I hope it's not gonna be any robbery today because it's raining and they are afraid of rain,'" Szabla said.
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Police said this is the second time this month, this particular Walgreens has been targeted by a knife-wielding offender. Just five days ago, police said the store was subject to an armed robbery.
"I myself witnessed it several times," Szabla added. "Alcohol, cosmetics. People just walk in, take things and they walk out and these employees cannot do anything."
Police said Tuesday they believe Williams may have been connected to that incident and a similar incident at another nearby Walgreens.
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Walgreens spokesperson Phil Caruso said in a written statement: "We are grateful to Chicago police and law enforcement for their efforts and will continue to work with authorities. The safety of our customers and team members is our top priority. We are continually evaluating our security measures in all our stores. The store is expected to reopen tomorrow morning with additional security measures."
Anyone with information is asked to call (312) 746-5446 or visit home.chicagopolice.org.