Process.Close() is not terminating created process,c#-Collection of common programming errors

I’ve written a C# application which uses System.Diagnostics.Process class to create a process, using

 Process P1 = new Process();
 P1.FileName = "myexe.exe";

and other proper settings.

I’ve linked it to an exe file which runs for about 10 minutes. (I’m writing program to measurer runtime of programs). Now in between i want to abort the running process. So I wrote in the cancel button’s event,

 Process.Close();

But in the task manager i still see myexe.exe running, it doesn’t get aborted. What to do?