I have produced mocked up crime scenes very simply as the others have said. Broken bit of glassware with red food colouring or ink on it. Inky/bloody fingerprints. A few threads caught on a nail or splintered piece of wood. Fingerprints on pieces of glassware - rubbing a bit of vaseline on your finger first helps make good ones. Dust with a bit of aluminium powder and a small paintbrush. Collect with sellotape. To collect their own fingerprints, get them to scribble lots of graphite from a soft pencil onto a piece of paper, run their finger over it and then roll it onto a piece of paper with boxes for each print. You can also do palm prints this way. For fake blood you can mix food colouring with cornflour and golden syrup. With a few syringes this works very well for blood splatter investiagation. We got the recipe from the upd8 website (Death of an Angel). For powders they find, you can get them to do flame tests. http://www.thinkforensic.co.uk/index.php?id=1 This website may help you out with a few ideas too.