Now, that mother is speaking out for the first time, in part, to highlight just how special her kids were.
"My children were amazing and three beautiful little souls who didn't deserve this," said the children's mother, Debra Karels.
WATCH: Mother of 3 children allegedly killed by father speaks out for first time
Jason Karels, 35, had his bond set at $10 million by a Lake County (IL) judge, but prosecutors plan to petition for no bond at a hearing that could happen later this week.
It appears Karels and his wife had an ongoing custody battle. The children had been dropped off with him for the weekend as part of their agreement.
"Mr. Karels left a note in the home, which stated, 'If I can't have them, neither can you,'" Lake County State's Attorney Eric Rinehart said.
Police said a mother, who was supposed to pick up her three children from her estranged husband, contacted them around 1:40 p.m. Monday to perform a well-being check inside a home in the 200-block of East Camden Lane in the Sutton-on-the-Lake subdivision. When police arrived, they found the three children, who were identified as 5-year-old Bryant, 3-year-old Cassidy and 2-year-old Gideon Karels by the Lake County Coroner's Office, dead. The coroner's office said preliminary autopsies indicate they died from drowning.
"I talked to the kids the night before. I said, 'I love you so much. I can't wait to see you tomorrow.' And the next day they're gone," Debra said. "He knew that nothing mattered to me more than those children. He took them away from me because he knew it would hurt me the most."
You can hear the anguish in every syllable.
"I just wish I was there for them that day," the children's mother said. "I wish I was there to grab them before this all happened."
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Authorities said the children were drowned in the bathtub by their father at his home on Camden Lane. Their bodies were found in a bedroom.
Prosecutors said Karels drowned them one by one.
Lake County Board Member Dick Barr set up a GoFundMe for the mother.
Her quavering voice described the unthinkable for any parent. The mother recounted her three children lost in an act of deadly brutality after Debra sought a divorce, imploring her husband to get help for what she called his suicidal thoughts and mental illness.
"She wants people to know who they were, and she wants people to remember them," Barr said. "I'm gonna tell you, we're getting hundreds of emails from people saying 'What else can we do?'"
Debra described 5-year-old Bryant as "the smartest kid in the world" who wanted to be an astronaut, 3-year-old Cassidy as her "mini-me," and 2-year-old Gideon as simply "the sweetest little boy."
Police arrested Karels when he crashed his Nissan off Interstate 80 near Joliet after a high-speed chase with police.
"After the crash, Karels made statements to police officers involved in the chase and wearing body-worn cameras indicating he was responsible for the deaths of the children at the Round Lake Beach home," Round Lake Beach Police Chief Gilbert Rivera said Tuesday. "He also said he attempted to commit suicide several times after the deaths of the children but was unsuccessful during these attempts."
His blood was allegedly found inside the home.
"I tried so hard," Debra said. "I never thought he would do something so tragic like this."
After being hospitalized, Karels, who has been charged with three counts of murder, was taken to the Lake County Jail.
"I don't know that anything could've stopped this or if there were any early indications of it," Chief Rivera said. "As I mentioned, we were not familiar with this family nor with the house."
The Illinois Department of Children and Family Service had no previous contact with the family, an agency spokesman said Wednesday.
The father has no known criminal history or history of drug use or mental illness, Rivera said.
"So many people told me, do not let him have them. Do not let him have them because he's mentally ill. To leave him constantly, but I was mind manipulated to believe he was a good person," she said. "Trust your gut. Trust what people say."
The community is also struggling to understand this senseless act but is now rallying around the mother of those children with a growing memorial outside the home.
Many gathered Wendesday night to remember the young lives lost.
"The deaths of these young children have crushed me, and I'm sure they have you as well," said Round Lake Beach Mayor Scott Nickels.
If Karels posts bond before that next hearing, he's supposed to stay away from the mother of those kids.
"Stick to your guns. Keep your kids because that is all that matters because some people out there don't care about them," Debra said.
The family had moved to the Round Lake Beach home five years ago, Rivera said.
The community continues to rally around that mother, raising more than $70,000 for funeral and other expenses.
If you feel suicidal or you're worried about someone you know, you can call the National Suicide Prevention Lifeline at 1-800-273-8255. You can also text the Crisis Text Line by messaging TALK to 741741.
For more information, visit suicidepreventionlifeline.org.
Sun-Times Media contributed to this report.