William R. Zientek has been charged, Barrington police said Tuesday. He lives in the same block as where the incident occurred.
Dr. Olga Duchon, 42, of Vernon Hills spoke to a Ukrainian medical association in Wheeling Sunday afternoon.
Her family had planned to celebrate after the event.
They said Duchon told them she planned to first stop to talk to the father of her young daughter.
They never heard from her again.
"She said, 'ladies, just go ahead. Wait for me. I need to make a quick stop, and I'll come join.' And she never did," said Yuliya Abushevich, a family friend of 20 years.
Duchon went to a townhome in the 400-block of West Russell Street in Barrington.
About 5:40 p.m. Sunday, police were called to the home.
Duchon had been shot in the chest.
She died at a nearby hospital soon after.
Neighbors said they saw a man being taken into custody Sunday.
Officers also apparently removed a child from the home.
Family said Duchon met Zientek several years ago.
Duchon filed an order of protection against Zientek in McHenry County in November of 2021, but it was terminated just weeks later.
Their daughter is now in the custody of Dr. Duchon's family. She's set to turn 4 next week.
"I just can't believe, we're preparing for her birthday together, that she won't be here for that. She was an incredible mom, always reading, always taking her to museums, educating her beyond her age," Abushevich said.
Abushevich said she and Duchon immigrated to the United States from Ukraine around the same time in the early 2000s.
"Worked multiple jobs, focusing on her medical education, became a doctor here, supporting her family, her mom and dad, as well," Abushevich said.
Dr. Maria Hrycelak said Duchon was only scheduled to speak for around 40 minutes Sunday, but gave an hour and a half of her time.
"Knowledgeable to the max, I mean she was so interactive with the audience," Hrycelak said.
She said they parted at 4 p.m.
"Then, an hour and a half later, she's tragically killed. I mean, it's stunned. Anybody who was there was just stunned because the connection that you got in that hour and a half of her talking was just, I can't explain it," Hrycelak said.
Duchon's friends said they feel a sense of relief knowing Zientek is facing a murder charge.
A GoFundMe has been created to honor Duchon and support her daughter.
Barrington police classified the shooting as a domestic-related incident, and said the general public is not at risk.
Barrington police say the investigation is continuing, and have not provided details of what led up to the shooting.
They did not confirm whether anyone remains in custody, but said Zientek is due in court Wednesday.
The Cook County Major Crimes Task Force is also investigating.
You can contact the Illinois domestic violence hotline at 1-877-863-6338 click here for more information.