Crime scene for DS Please can someone help?

Love this game! But the tools are starting to annoy me... or is there a glitch? I'm on mission 1 and I cant cut the material from the trousers! Is there a special way to use the scalpel? Its taken me soooo long and I'm getting tired of losing my job over and over. ANy hints will be appreciated :)

I've replied in the other thread but basically run your scalpel along the lower edge of the arrow that pops up. Another handy tip is to continually save so that you don't lose what you have done if you lose your job! Hope ths helps. And ther tools are annoying me too!