Paper or Plastic…How is Evidence Packaged?
Sealed paper evidence bag
Ya know, I don’t think I’ve ever seen a TV CSI package evidence in a paper bag. After all you can see the bloody gun unless it’s in clear plastic right. Well, what works for television doesn’t really work in real life. This is one of those “devil is in the details” type articles for your writing. As a general rule, criminalists don’t like wet evidence. Whether is blood, water, urine, or soda pop; wet evidence doesn’t do well in sealed plastic bags. That’s because plastic can not breathe, and if it can’t breathe it will grow mold.
This is especially important when you consider that some cases make take years to go to trial. That’s a lot of growing time for mold. Add to that the backlog of cases each analyst may have and you get a real recipe for disaster. Imagine an expert opening an evidence bag to do critical testing only to find a petri-dish of blood fed mold…yuck! For that reason most evidence is packaged in paper or cardboard just to be safe. Plastic can be used for dry documents or even dried bloodstained clothing, but only after dried.
Moldy shoes from sealing in plastic while still wet
Crime labs even have special cabinets where items can be stored safely while drying. These cabinets are very handy to separate clothing from say the victim and suspect, or items from separate cases. As you might imagine, medical examiners also use these cabinets as they deal with a lot of “wet” evidence.
Evidence drying cabinets
In your story you could use this type of event as a major setback your characters must overcome. Image a suspect who gets away with a crime because crucial evidence was moldy. Will your characters be able to find other evidence before he strikes again? What about an innocent man who petitions to have evidence i the case tested with some new technology only to discover it is irreparably damaged. Any way you spin it, packaging can have long term implications for your case.
Posted on June 17, 2011, in The Crime Laboratory and tagged detective, evidence drying cabinet, evidence packaging, fiction, forensics, murder, mystery, thriller, tom adair. Bookmark the permalink. 4 Comments.
Very interesting, f4f. I saw a movie on TV once where the crime scene evidence was in padded paper envelopes. My ignorance flared when I commented that they should be in plastic bags. Little did I know that the director had it right, and I was *cough choke* wrong.
Thanks for the information. More and more, I am tempted to write a crime story…maybe even a novel
Don’t beat yourself up. As you can tell from the article there are some in law enforcement who think the same thing. Good luck on your writing and let me know if you have questions.
This is a wonderful site and I’m so glad I was led here through one of my writing groups. I am published in romantic suspense, though I’m writing in another genre at the moment. I hope to get back to RS soon.
I have some questions about the above post. What about the case of an officer of the law who comes across evidence they would like to check. I realize this would break the chain of evidence and not be admissible in court. But, let’s use the scenario where are main character wants prints off of some object and doesn’t have a paper bag handy. What kinds of items can be used in a pinch? A handkerchief? A tissue? Would these smudge the prints?
Thank you so much for sharing your expertise.
Thanks for the nice comments Gabriella. To be clear, we sometimes do use plastic bags to transport “wet” (i.e. bloody) items back to the lab for drying. Suicide notes, ransom notes, etc might also be placed in plastic temporarily so others (district attorney, Coroner, etc can see the wording). In those cases however the plastic bag would not be sealed. That also means that the collecting officer needs to remain with the item for the chain of custody as you alluded. Tissues, handkerchief, etc do run the risk of smudging prints. Actually, I should write a post about how criminalists handle objects to minimize this risk. A CSI or detective will have latex gloves to handle items. Prints on paper will not get “smudged” but if handled with bare hands, you would run the risk of leaving your prints which might overlap the ones you’re looking for. I hope this helps. Tom