Fans did double-takes when Selena Gomez and her mom, Mandy, showed up at a true-crime event in Chicago.

The star wasn’t at CrimeCon’s CrowdSolve gathering to promote any project — she’s a devotee of the subject and was helping to crack a real-life mystery. The event focused on solving a 1981 case out of Ohio.

A spy said of the star and her mom: “They were always together and totally engaged in the work … taking notes and really getting into the idea that we could help this family get justice.” The duo also attended a dinner with a forensic hypnotist.

Another spy added: “It was cool to see that even celebs can be into true crime, like us. Everyone was very respectful and it looked like they were having a really good time.”