I really liked the tone that you used. Reminded me of someone telling the story in a pub after the incident. Have you considered first person narration for this? It would be interesting to see. The story is good as is but its always good to explore new ideas.
I would also suggest that you cut out some excess.
Here is how I would re-word the first paragraph.
Two thieves walked through a graveyard taking each step with care.
One of them, a big fat man called Blackie carried two shovels. His partner, Claude was of medium height. A skinny man with blonde hair and stubble.
I would suggest that you look more into " showing the story" rather than
"telling". To do this I would suggest some exercises from the BBC website
"Get Writing". Most of the lessons on there are free and they really helped me out a lot.
Here is a link
DISCLAIMER: This is no way a "wrong or right" critique, just my observations and suggestions.