CHICAGO (CBS) -- A suspect was charged Tuesday afternoon with stabbing an employee to death at a Walgreens drugstore in Wicker Park over the weekend.
Police said Sincere Williams, 18, was charged with the Sunday morning murder of Olga Marie Calderon, 32, who was stabbed to death at 9:30 a.m. that day after she reported for work at the Walgreens at 1372 N. Milwaukee Ave.
Williams is expected to appear in bond court on Wednesday afternoon.
Area Five Cmdr. Eric Winstrom said Williams entered the Walgreens intending to rob the store at knifepoint. He approached Calderon, who was stocking shelves at the time, and grabbed her around the neck, Winstrom said.
It appeared that Calderon tried to push Williams away, and at that point, he began stabbing her multiple times, Winstrom said.
Police told CBS 2 Investigator Megan Hickey they are not aware of any prior interaction between Williams and Calderon.
"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," Winstrom said.
Williams discarded the knife and his clothing in a nearby yard, and detectives found it all, Winstrom said. Area Five detectives reviewed private and city surveillance cameras and were able to trace Williams all the way back to the apartment complex in the 1400 block of North Sedgwick Street in the Marshall Field Garden Apartments, where he lives, Winstrom said.
Detectives canvassed the complex and identified Williams, and arrested him at his apartment with the help of Near North District police personnel, Winstrom said.
Frederick Watkins lives in the same apartment complex.
"They were looking in garbage cans," he told CBS 2's Charlie De Mar. "They were dumpster diving, looking for I guess the weapon or something."
Watkins said he saw the CPD looking for evidence in the trash Sunday night. He also said he has interacted with the now-murder suspect before.
"Quiet, kept to himself, because he didn't interact with the guys his age in the neighborhood," Watkins said.
Williams had been treated for an injury to his hand at Northwestern Memorial Hospital after the attack, but before he was arrested, Winstrom said. He could not say whether anyone found that suspicious at the time.
Winstrom is also believed to be behind two other robberies – one of them at the same Walgreens and the other at another nearby.
Police said in both incidents, a man, armed with a knife with a red handle, went into a pharmacy and demanded money. In one case he successfully took money from the store. He fled the scene in both incidents.
One of those incidents took place at 7:20 a.m. last Wednesday, a short walk away from the Wicker Park scene at a Walgreens at North and Western avenues. The other took place 17 minutes later at the very Walgreens on Milwaukee Avenue where Calderon was murdered.
Winstrom said the description of the knife and mask in those robberies matched those recovered from Williams, but the investigation continues.
The Walgreens on Milwaukee Avenue remained closed Tuesday night. The flower memorial has been growing by the day outside the Walgreens where Calderon worked. Walgreens employees were left shaken.
"I work not too far from here, so when I found out what happened, my heart was just really broken," said Walgreens employee Jennifer Montanez.
Friends and former coworkers said Calderon was a hard worker – friendly and talkative. She was also the loving mom of a 3-year-old boy and an 11-year-old girl.
Chief of Detectives Brendan Deenihan emphasized the horror of an attack on "a young lady going to work, doing everything she was supposed to do trying to raise a family, and this was an unbelievably tragic incident."
While Calderon's friends, family, and coworkers got answers Tuesday as police announced charges against Williams, they said they were still no answers that made sense.
"I don't know who would want to do something like that to such a beautiful person," said Calderon's friend, Jasmine Johnson.
Calderon's family said she always put others first, and Johnson knows that well. She was recovering from a major surgery earlier this year, and she said her cashier at Walgreens - Calderon - went out of her way to help her.
"She just encouraged me that everything would get better for me. You don't find people like that every day," Johnson said. "She was just a very nice person that I could talk to about anything."
And they became instant friends.
On Tuesday night, the Milwaukee Avenue Walgreens store remained closed – and her community continued to ask why.
"We go to work and we don't know if we're going to come back," Montanez said, "and it's a really sad time to live in."
Deenihan noted that there were no eyewitnesses to the attack, and emphasized that technology and the review of hours of surveillance video were vital in solving the crime. He also thanked the Cook County Sheriff's office for lending a bloodhound that helped track Williams.
Williams is charged with first-degree murder. He is due for a bond hearing on Wednesday in Violence Court (Br. 66).
CBS 2's Charlie De Mar and Investigator Megan Hickey contributed to this report.
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