How can I focus a particular item in ListBox in WPF

Question

Hi,

  I have a listBox whose elements are binded using ItemsSouce.
Now in the code behind I want to move the focus to the 3rd item in the listbox.
Can somone tell me as to how can I acheive this?
I think that once we get the access to listboxItem than we can easily set the focus by calling <listboxitem>.Focus(). But now the question is how can I get a particular ListBoxItem object for a binded ListBox?

Even though it looked quite obvious to me, I didnt found a solution.