A dry artist brush is useful for brushing off loose dust. That's why its used for finding fingerprints. The powder sticks to the oily pattern left by the finger, and the loose dust is brushed away. Viola', a fingerprint!
Using a brush as an oiler is also possible, for very small areas. Could also be used to spread (paint) the surface with oil or some other liquid.
The typical artist brush is not good for scrubbing, like the "toothbrush" is, although some of the larger flat point brushes will do ok.
I have found all the "forensic" shows on TV to be a mixture of fact and fantasy, heavy on the fantasy. And not just the plot. I used to like "Law & Order" (still enjoy it mostly), because I liked the "realistic" seeming way they handled the law, until I had seen enough of the show to realize that they were treating the law just the same way they treated guns (unrealistically) and everything else. The episode that pushed it over the edge for me was one where a rape victim was at the range (in NYC) with a Desert Eagle and a 15rnd magazine!
The cop Olivia tells her that 15rnd mags are illegal in NYC. She says "oh, I didn't know that", and gives Olivia the mag, and continues on with her shooting. Later in the episode, she kills her rapist, when he tries again, with a pair of scissors!
I like the Closer, but they also have been getting in anti-gun digs and pure BS lately. The Lt who is the techno geek on the squad can tell that 9mm cases he finds at the crime scene (as he puts them in an evidence bag) were fired from a Tec9. Again, nothing but writer's fantasy!
I have learned never to expect accurate treatment of anything gun related, legal,sexual, medical, or even the basic laws of physics from my TV! Even the History Channel screws up on occasion!
The best thing about these kinds of shows is the music! At least some of it is real.