I was looking at the Pinterest mentioned here and found a photo of the suspect: https://pl.pinterest.com/pin/67131850687569582/
See the logo in the top right it’s a clear rebrand of “Muslim Corps of the Caucasus”.
Coincidentally Kirk starts talking about Muslims being dangerous and he is killed?

Even if he is not the killer might be worth looking into.

You can try geolocate the shop the photo is in.

Found their yt channel, you can try to see if there are any clues on US activity:
https://youtube.com/@warforfreedom?si=Xse3LZFehEi-8bJp