Kill process that was started from a thread

Question

Working with .Net 3.5 WPF app. In the app, I'm opening five threads and each thread executes a PowerShell script. Where I'm having trouble is, how do you kill all PowerShell instances that are started?

        var threads = new List<Thread>();

        for (int i = 0; i <= toProcess; i++)
        {
            PowerShellWork work = new PowerShellWork();

            work.aId = aId;
            work.thread = int.Parse(argList[i].iThread);

            ThreadStart threadDelegate = new ThreadStart(work.Execute);
            Thread newThread = new Thread(threadDelegate);
            newThread.Name = associId;
            newThread.Start();

            Thread.Sleep(1000);

            threads.Add(newThread);                
        }

        foreach (var thread in threads)
            thread.Join();

---

class PowerShellWork
{
    public string aId;
    public int thread;        
    public void Execute()
    {
        string shellPath = "powershell.exe";
        StringBuilder sb = new StringBuilder();
        sb.AppendFormat("\"& '{0}'\" ", @"C:\PS_Scripts\PSupdate.ps1");
        sb.AppendFormat(" {0} {1}", aId, thread);
        string result = ExecuteCommand(shellPath, sb.ToString());

    }

    private static string ExecuteCommand(string shellPath, string arguments)
    {
        arguments = "-noprofile " + arguments;
        Process process = new Process();
        var info = process.StartInfo;

        process.StartInfo.UseShellExecute = false;
        process.StartInfo.FileName = shellPath;
        process.StartInfo.Arguments = arguments;
        process.StartInfo.RedirectStandardError = true;
        process.StartInfo.RedirectStandardOutput = true;

        process.Start();

       //process.Kill();

        var output = process.StandardOutput;
        var error = process.StandardError;

        string result = output.ReadToEnd();
        process.WaitForExit();
        return result;
    }
}

---

Edit* This is how I solved my issue. Please let me know if you know of a better wway.

    private void btnCancel_Click(object sender, RoutedEventArgs e)
    {
        worker.CancelAsync();
        ConfigurationManager.AppSettings["StopProcess"] = "Stop";

    }

In my PowerShellWork class

        process.Start();

        do
        {
            if (ConfigurationManager.AppSettings["StopProcess"] == "Stop")
            {
                process.Kill();
            }
        } while (ConfigurationManager.AppSettings["StopProcess"] == "Run" || !process.HasExited);