Kill external process in Unity

I’m trying to open an external program in Unity and kill it afterwards by using this code:

Process myProcess;
string path;

path = Application.dataPath + "movie.avi";
myProcess = new Process();
myProcess.StartInfo.FileName = "C:\\Program Files\\Windows Media Player\\wmplayer.exe";
myProcess.StartInfo.Arguments = path;
myProcess.Start();

To kill it:

myProcess.CloseMainWindow();

Opening the file works fine, but I got the following error when Unity tries to kill it:

SystemException: No process to kill.

How to solve this? Thanks.

Finally I got a solution:

foreach (Process p in Process.GetProcessByName("wmplayer")) {
   p.CloseMainWindow();
}

Try:

myProcess.Kill();

Instead of:

myProcess.CloseMainWindow();