ShellListView deselect

I am trying to use the TShellListView component from the Demos.  I am trying
to "deselect" an item when in "report" mode.  I created an event handler for
the mousedown event and checked for the control key.  Then I tried to set
the ItemIndex to -1 so that nothing was selected.  That caused an access
violation exception that I couldn't trap.  I assume the problem is in the
windows control.

Any ideas how to "unselect" all the items?