The Will County Sheriff's Office said the suspect is an 18-year-old Joliet man. ABC7 is not identifying him because he has not yet been charged in connection with the deadly mass shooting.
Police responded to a shooting in the backyard of a home around 12:40 a.m. Sunday in the 1000-block of East Jackson Street.
More law enforcement officials arrived and saw multiple people who had been shot in the backyard and at nearby houses. More shots were heard while first responders were treating those who had been wounded, police said.
At least nine people were injured and taken to local hospitals. Two people died as a result of their injuries on the scene, police said.
Holly Mathews and Jonathan Ceballos, both 22 years old, were identified by family members as the two people fatally shot.
Mathews was studying to be an arborist at Joliet Junior College and had just gotten engaged two weeks ago while on vacation in Utah. But while she was out with two girlfriends celebrating Halloween Saturday night at a house party, her loved ones said she was shot and killed.
A witness, who only wanted to be identified as Nathan, said he was there, along with much of his family and friends from high school.
Ceballos was his childhood friend.
"He was a great dude. Straight-A dude, great at sports -- just a genuinely good person. I knew his dad. His dad coached me," he said.
Mathews and her friends were there only briefly and had, by all accounts, decided to leave when police said two men standing on the porch began firing into a crowd of people gathered in the backyard.
Mathews' family spent hours at her visitation Friday, finding some solace in the arrest, but still reeling in pain.
"It means justice will be served... and he'll be off the streets, not hurting more kids anymore," said Sharyl Mathews, the victim's mother.
Her fiancé, Adam Gregurich, also found some comfort in the news.
"Made me feel a little better, but now just needs to be carried out hopefully," Gregurich said. "Hopefully it's the right person."
Mathews' fiancé said she did not know the suspect, who authorities say faces multiple unrelated charges and "is being held on a $1 million bond."
Meanwhile, Mathews' family mourns a fearless young woman, whose off-roading rig now a memorial.
"I just want to crawl inside with her and hug her and tell her how much I love her," her mother said.
Visitation for Mathews continues Saturday before her funeral. Ceballos' visitation begins on Sunday.
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Four more people suffered life-threatening injuries.
The first shooter is described as an average-sized male suspect with facial hair, wearing a red hoodie, a black flat-billed hat and dark pants. The second shooter is described as an average-sized, male suspect wearing a yellow hoodie and ski mask.
Anyone with information, cellphone pictures or video of the party or potential suspect information is urged to contact the Will County Sheriff's Office at 815-727-8574, extension 4930, or via email at firstname.lastname@example.org.
Anonymous tips can be submitted on the Will County Sheriff's website at www.willcosheriff.org/enforcement/submit-a-crime-tip or on the Will County Sheriff's Office App that is available in iOS and Android.
You can also contact Will County Crime Stoppers by telephone at 800-323-6734 or at www.crimestoppersofwillcounty.org/submit-a-tip/.