Around 1:30 a.m., police responded to a 911 call. The off-duty officer had been critically wounded after being shot several times and 45-year-old Kathryn Romberg had been shot to death.
Romberg was a realtor who also worked for the Department of Children and Family Services.
The officer was rushed to Mount Sinai Hospital.
"The officer is in the hospital. He is in critical. His family has been notified. The investigation is continuing," said Supt. Jody Weis, Chicago Police Department.
Weis spoke with reporters briefly outside the hospital early Wednesday morning, but did not release much information about the shooting.
"It appears to be an attempted robbery," said Weis. "That's all we really have at this time. He's just a victim."
Neighbors, however, say they are suspicious about the shooting. They say the officer and the woman had been yelling at each other while sitting in the parked SUV.
"I know that they had been arguing for a while, I think for a few hours. My neighbor had called the police, that someone was arguing. I know the police came by and they talked to them, then they left," said Sue Naiden, neighbor.
Brittany Russell said she called the police to report the loud argument outside, then called again after she heard gunfire.
"Next thing I know I woke up, heard some gunshots at 1:30. It was the same car, so I called again. The driver started laying on the horn, trying to get someone's attention, and I heard him saying he was shot," said Russell.
"And he was saying, you know, 'Somebody, I'm dying. Somebody call an ambulance I'm dying,'" said Naiden.
Chicago police confirmed a 13th District beat car responded at 12:17 a.m. to a report of "screaming males in the alley." After speaking to the SUV's occupants, the officers left, reporting that "there was no further action required."
At 1:34 a.m., a different beat car responded to the report of "possible shots fired and loud horn."
Neighbors say Romberg had lived in the apartment for about three years with her daughter, who is in her early 20s.
"She was very nice," said Naiden. "She worked to help kids that were in bad situations. She was always willing to help around here. Her daughter here is going to be by herself now."
The off-duty Chicago police officer is a 23-year veteran of the force. He is a detective with the bomb and arson unit. He is in critical condition at Mount Sinai.
Sources told ABC7 that the officer's service weapon was found inside the SUV. Sources also say that it had not been discharged.
Chicago police canvassed the neighborhood, hoping more witnesses would come forward. So far, police have not made any arrests.
Soto lives on the Southwest Side with his wife and disabled brother.
"If you needed anything done, you had any questions, he was always there to help you," said Carol Moshol, neighbor.
The relationship between Detective Soto and Romberg is unclear.
Police said they are looking for a dark-colored Ford Taurus in relation to the case.
Sources say Soto was able to give some description of the suspects before he lost consciousness. He had yet to regain consciousness Wednesday night.