PID from window ID/name

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http://unix.stackexchange.com – I need to kill a process that spawned a window which seems to have no PID associated with it. At least that is what xdotool says: ~$ xdotool getwindowpid 79691780 window 79691780 has no pid associated with it. wmctrl -lp prints 0x04c00004 0 0 N/A Window name xprop _NET_WM_PID says _NET_WM_PID: not found. I'm out of ideas, is there really now way of telling which process owns this window? (HowTos)