The state's attorney's office is now reviewing the evidence against a suspect.
ABC7 first reported police had a man in custody on Wednesday night. Now ABC7 has learned more exclusive details about the case.
A Chicago man believed to be 38 years old is expected to face charges in O'Laughlin's death.
"We feel very confident about the case and about the individual that's in custody right now," said Cook Count Sheriff Tom Dart during a news conference late Thursday night.
"As far as this crime is concerned, I think we can all rest a little bit easier tonight," said Indian Head Park Police Chief Frank Alonzo.
Sources tell ABC7 that blood DNA evidence is a key part of the case and that O'Laughlin's blood was found on the suspect's clothing. ABC7 is also told that he apparently hailed a cab after the crime, possibly from a nearby convenience store, and he tried to pay the cab driver with an odd set of coins. The day after the killing authorities released pictures of coins similar to the ones missing from the family's home.
Sources also tell ABC7 that the suspect attempted to use Kelli O'laughlin's cell phone to call her mother. It's unclear whether he was successful.
Sources have called the suspect a Chicago gang banger. Along with being a parolee, the suspect has been arrested at least five times for petty drug offenses, aggravated battery and possession of a stolen vehicle. He also has at least one year left of probation.
Earlier in the day Thursday during a brief news conference, police said investigators have been working "feverishly" on this case since last Thursday when it happened. Since then the O'Laughlin home has been a crime scene.
Kelli O'Laughlin, a freshman at Lyons Township High School, had been stabbed. Gold coins were taken from the home, and investigators suspect that the person with those coins would have information about the murder.
For the first time Wednesday O'Laughlin's father John released a statement on behalf of wife Brenda and their three children:
"We are truly overwhelmed and touched by the outpouring of support we have received from the community and all those who knew and loved Kelli. We are so grateful to everyone who has offered their support and condolences in this difficult time."
Visitation continued Thursday for Kelli O'Laughlin. Her funeral is planned for Friday.