You all know John hates that damn White Sox gnome. (Motive -- check)
And you all know John threw him to the ground resulting in a broken gnome foot. (Capable of specific actions -- check check!)
After our fabulous nanny masterfully glued the gnome back together, somehow it ended up looking like this:
All evidence points to John.
And John doesn't have an alibi (nor could he tell you one at this point).
(The plot-twist confession: Mama did it.)