Wheel meet again

A security guard stops a man leaving a factory gate. The man is pushing a wheelbarrow with a hessian sack covering it. "Lets have a look under that sack" says the guard. The man obliges, lifting the sack - nothing underneath - the barrow's empty. "On you go" says the guard. Next day same thing, the guard stops the man and looks under the sack, same result, empty. After a week of this the man doesn't appear again, so the guard mentions it to a colleague at shift changeover. "Have you seen the guy with the wheelbarrow"? "No" says the other - "Not surprising - he's been dismissed, got the boot". "What for"? asks the first. "Stealing wheelbarrows" laughs the other.