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.
"She went to a party in Frankfort [and] was there until midnight," said Holly's mother, Sharly Mathews. "The party ended and one of her friends, the girl she was with, said let's go to this other party."
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.
"I just talked to her [Saturday] morning. She was going to come over today for Halloween and she was looking forward to it. We were going to carve pumpkins and the whole nine yards," Sharly Mathews said.
"She was just a young girl in a costume for a Halloween party. Lost her life for no reason. Absolutely no reason," added Holly's father, Stephen Mathews.
Will County Sheriffs officers said they were on the scene within minutes after a patrol sergeant heard 10 to 12 gunshots being fired just before 12:40 a.m. in the area of Jackson and Walnut streets and then saw over 100 people running east on Jackson Street, the sheriff's office said in a Facebook post Sunday.
Witnesses said the shooting took place in the 1000-block of East Jackson Street in the backyard of a home.
"As we were dancing on the back patio shots started going off from the porch and we were like what? I threw my girlfriend to the side, to the floor and she fell and I fell with her. And as I got back up I seen that everybody started running and as soon as I got the chance, I just started running too, "Everyone was there having fun and all of a sudden as we're dancing on the back patio, shots started going off from the porch," "You could hear the bullets ricochet and whistle."
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.
Over a dozen people were injured and taken to local hospitals. Two people died as a result of their injuries on the scene, police said.
RELATED: 1 dead, 9 injured at Texas Halloween party shooting; Search for gunman ongoing
Four more people suffered life-threatening injuries.
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.
RELATED: Chicago police shooting: No one hurt after officer shoots at person firing gun in East Garfield Park
Will County Sheriff's deputies believe a Halloween party was being held at the home, and the shooting took place outside near a DJ booth in the backyard. There were about 200 people at the party, police said.
Witnesses said there were two shooters. The shooting reportedly took place from an elevated position on a porch looking down over the crowd.
"It was horrible. You could hear the bullets ricochet and whistle," Sandoval said. "Not everyone there was bad people. Some who got hit were innocent."
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.
Law enforcement officials remained on the scene Sunday morning. The Will/Grundy Major Crimes Task Force was activated to help with the investigation.
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 email@example.com.
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/.