I was getting thrown by this too - are you examining the right tire tracks? I did the investigation a bit in a different order, cross-checking the walkthrough, and was ending up examining the tracks in "Ravenview Forest" rather than "Forest Path" (where Gumshoe is).
Viewing post in A Turnabout to El Dorado comments
Yup, I examined the right ones. Maybe if this helps I downloaded this from https://phoenixwrightaceattorney.weebly.com/fan-games.html, so maybe the version I haves broken, but idk. I've gone back and retraced my steps too and nothings happened. I'm thinking just loading to the start of the investigation and going through it again.