A registered sex offender allegedly kidnapped a young girl, left her lifeless body behind and strangled her younger sister in a random attack around noon Saturday. 

The two young girls - ages 10 and 6 - were playing outside their suburban Rockford, Illinois, home when a man, who was later identified as Antonio Monroe, 44, allegedly grabbed them, police said.

Less than 40 minutes later, an unidentified man found the 10-year-old unresponsive and flagged down police officers, who tried to save the 10-year-old, but CPR efforts were unsuccessful. 

The victim was identified on a GoFundMe page as Destiny Huggins. She was pronounced dead at an area hospital. 

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Antonio Monroe mugshot

Antonio Monroe, 44, a registered sex offender, allegedly kidnapped a 10-year-old girl and strangled her to death. (Illinois State Police)

"From the time my phone rang yesterday in regards with this incident, my stomach has been in a knot," Rockford Police Chief Carla Redd said, according to WIFR.

Huggins' younger sister, who was allegedly strangled during the random attack, told her mom that a man grabbed her sister while they were playing the neighborhood of 9th Avenue.

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The jarring crime sparked a full-court press by the Rockford Police Department, including K-9s, who found Monroe a couple of blocks away from the unresponsive child near the intersection of 9th and Woodruff avenues in the city, police said.

"From the time my phone rang yesterday in regards with this incident, my stomach has been in a knot," Rockford Police Chief Carla Redd said, according to WIFR.

Monroe allegedly fought with officers during the arrest and was taken to a local hospital for "an unrelated issue," Rockford police said.

Destiny Renee Huggins, 10, memorial photo image

Destiny Renee Huggins, 10, was allegedly murdered by a sex offender in Rockford, Illinois, while she played with her younger sister around noon on July 8. (GoFundMe)

"We’re not living in a time where you just leave your kids outside playing and no one to watch over them," Redd said, according to the local news outlet. "Kids aren’t doing anything wrong, but unfortunately there’s individuals out there that will cause harm to them."

The younger sister was treated at an area hospital for strangulation-related injuries and released later the same day, Chief Redd said. 

"I have a 7-year-old daughter, and I just don’t understand how someone has this in their being to do something like this to something as sweet and beautiful as that," Rockford Mayor Tom McNamara said during a press conference. 

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Chief Redd said "sick individuals" changed the city. 

"Growing up in the city, I had the ability to stay outside and play until the street lights come on," the city's police chief said. "Unfortunately, that’s not the case anymore due to sick individuals that manage to make their way into the community."

9th avenue, rockford, illinois street view

A 10-year-old girl was kidnapped and killed while playing with her younger sister outside a home on the 1200 block of 9th Avenue in Rockford, Illinois, Rockford police said. (Google Street View)

Monroe was transported to Winnebago County Jail and booked on charges of first-degree murder, attempted murder, two counts of kidnapping and aggravated battery/strangulation. 

"This is a real life nightmare with a real life monster," McNamara said.

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More charges may be filed, according to police. 

Monroe is a registered sex offender after he was convicted of sexually assaulting a 19-year-old victim when he was 31 in Peoria County, about 140 miles south of this week's alleged kidnapping and murder in Rockford, a suburban city about 90 miles west of Chicago.