Hey DIESEEEEEL,
In this kind of situation where the player did change his name and you can't find him anymore there is one thing you can do, always type on chat /pinfo 1300 when the accident happens, which then it will show their TMP id and steamID64.
Now the good thing is every user you see on the road their details are saved in your documents
If you head to "Document's/ETSMP/logs/ you will see a lot of files such as "log_spawning" "client logs"(which you don't need to look on this one) and then there is also "chat log", if you remember the exact date of the accident you can find the "log_spawning" and search the user's name