The text has been deleted since, but this is what happened based on what I read of the post before it was deleted and OP's responses.
Remote worker uses personal computer to connect to VPN and RDP on work PC. Remote worker bought Xanax on personal computer. IT illegally installed monitoring software on worker's personally PC and took screenshots of the employee's receipts of buying Xanax. OP comes in to ask if they can fire the employee.