Framed.

Framing someone with a crime is easy. I've actually done it here, without even trying to. All you need to do is the set-up. Demonstrate that a person has motive and is capable of specific actions.

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:

Now, whodunit??

All evidence points to John.

And John doesn't have an alibi (nor could he tell you one at this point).

Framed.

(The plot-twist confession: Mama did it.)