taskkill /f /pid [PID]
For example:
C:\>sc queryex WSearch
SERVICE_NAME: WSearch
TYPE : 10 WIN32_OWN_PROCESS
STATE : 4 RUNNING
(STOPPABLE, NOT_PAUSABLE, ACCEPTS_SHUTDOWN)
WIN32_EXIT_CODE : 0 (0x0)
SERVICE_EXIT_CODE : 0 (0x0)
CHECKPOINT : 0x0
WAIT_HINT : 0x0
PID : 5604
FLAGS :
C:\>
taskkill /t /f /pid 5604