MELROSE PARK, Ill. (CBS) — Video obtained exclusively by CBS 2 shows accused Wicker Park Walgreens killer Sincere Williams breaking into a gun shop months before the attack, the owner says.

The store owner provided the video, and spoke at length to CBS 2’s Charlie De Mar.

The owner of Suburban Sporting Goods Guns & Ammo in Melrose Park said his gun shop was burglarized in May. He said Williams tried stealing 14 handguns.

RELATED: Employee Fatally Stabbed At Wicker Park Walgreens | Sincere Williams, 18, Charged With Stabbing Employee At Wicker Park Walgreens To Death

Williams, now 18, was arrested and charged with burglary at the time. And the gun shop owner said Williams should still have been off the streets at the time Cook County prosecutors said he murdered Walgreens clerk Olga Marie Calderon – and she should still be alive today.

Williams made it all the way from his apartment in the Old Town area to a bus stop in Melrose Park. He hopped off the bus early in May and walked straight to the Suburban Sporting Goods Guns & Ammo – armed with a hammer.

The gun shop owner said Williams, who was just 17 at the time, started smashing the front glass at least 20 times – breaking in and grabbing 14 handguns before he was quickly arrested.

No employees were inside the store, the owner told De Mar over the phone.

“That’s a pretty heinous crime,” the owner said. “These weren’t hunting guns. He wasn’t stealing to feed his family. These were likely going somewhere very bad.”

Williams, just two months shy of his 18th birthday, was charged as juvenile.

That didn’t sit well with the owner at all.

“I was kind of enraged. It’s like, here’s this kid that broke into a gun store and stole several firearms,” the owner said. “Just because he was caught, it doesn’t lessen the severity of the crime.”

Fast forward to August – the owner of the Melrose Park gun store said he was last notified that Williams violated the conditions of his electronic monitoring, but the court ordered that his monitoring bracelet be removed. The Cook County State’s Attorney didn’t object.

With Williams no longer under the court’s watch, he was allowed to enter the Walgreens at 1372 N. Milwaukee Ave. undetected Sunday morning. He is now accused of stabbing and killing store Calderon there.

“It enraged me that a woman is now dead and all they had to do was keep this guy in custody,” the gun shop owner said. “Obviously, it could have been prevented. He was in custody in May. I’m appalled that’s how our system works.”

The community is raising more than $66,000 for Calderon’s family. The mother of two was beloved by her customers.

“She was a kind, loving person,” said Cawanda Rice. For this to happen, it is so sad, because she was so sweet.”

Williams’ juvenile burglary case in the Melrose Park gun store burglary was still pending as of Thursday night.

Charlie De Mar