I don't, I don't know how to take one. For future reference, how do I do that?
long version:
https://www.skial.com/threads/collecting-evidence-in-tf2.47782/

short version:
"record demoname" in developer console to start recording
"stop" in developer console to stop recording
"status" in developer console to display user info like steamIDs (it is good practice to do this immediately after starting a demo)

easiest version:
To make it easy, you can copy and paste this into console:
Code:
bind "[" "record report; status; voice_loopback 1"; bind "]" "stop demo"
Hit your [ key when you play with him, and ] will end the recording when you're finished.
Hitting the [ key again will overwrite it, so you can re-use this if nothing happens for a while, or for future reports.
The demo will be in Steam\steamapps\common\Team Fortress 2\tf if you're on Windows.