Killing a process created with Python's subprocess.Popen()

Here is my thought:

First of all, I created a process by using subprocess.Popen

Second, after certain amount of time, I tried to kill it by Popen.kill()

import subprocess
import os, signal
import time

proc1 = subprocess.Popen("kvm -hda /path/xp.img", shell = True)
time.sleep(2.0)
print 'proc1 = ', proc1.pid
subprocess.Popen.kill(proc1)

However, "proc1" still exists after Popen.kill(). Could any experts tell me how to solve this issue? I appreciate your considerations.

Thanks to the comments from all experts, I did all you recommended, but result still remains the same.

proc1.kill() #it sill cannot kill the proc1

os.kill(proc1.pid, signal.SIGKILL) # either cannot kill the proc1

Thank you all the same.

And I am still waiting for your precious experience on solving this delicate issue.