Object reference not set to an instance of an object

Object reference not set to an instance of an object

The purpose of this program is to run through a range of pictureboxes and
set it's .image property to a particular image. I keep getting the error
"Object reference not set to an instance of an object". Coming from the
line that shows "DirectCast(Me.Controls(pic(i)), PictureBox).Image =
My.Resources.glass_buttonred"....Whats weird is if i move that code
outside of the for loop it runs just fine.
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs)
Handles Button1.Click
Dim pic(2) As Object
For i = 0 To 2
pic(i) = "picturebox" + Convert.ToString(i)
DirectCast(Me.Controls(pic(i)), PictureBox).Image =
My.Resources.glass_buttonred
Next
Label1.Text = pic(1)
End Sub