In “Whose fingerprint is that?” I chatted about the basics of fingerprint collection, using powders and brushes to uncover the evidence. Most of us think of doorways and murder weapons as the spots that cops look to connect suspects to a crime of passion. But, fingerprint detection is just as important on documents. Documents? Yup. There are scheming relatives who forge wills, less than loving spouses who murder for the insurance, bogus suicide notes, and the list goes on.
Jake was murdered for his $1,000,000. insurance policy, but how to prove the nefarious intent? Fingerprints. The problem is that fingerprint powder is messy and almost impossible to clean up. An important document could be destroyed in the search for evidence of foul play. Enter chemicals and alternate light sources (ALS).
Here are a few examples of the chemicals that deliver excellent results:
There is a protocol for testing with chemicals. If the prints don’t show up with one chemical, then it is possible to try several others, but this can only be done in a certain order:
If used in this order, the document won’t be compromised, even if the techs need to treat the sample several times over several days.
DFO reacts to amino acids in the prints. The suspicious document can be hung in a fume hood, saturated with DFO, then put it in an oven to bake for several minutes.
This DFO sprayed, baked sample doesn’t look like much, so the next step is to use an ALS to really ‘pop’ the print and make it photo ready.
Alternate Light Sources vary depending on the scene lighting and/or need to highlight the evidence. A few used in the field are: the ‘poor man’s ultimate light source’ (a mag light), black lights, UVC lights, lasers, LED lights, Ruvis lights (cost about $20K), and pure white lights. Each has a specific quality that the investigators can tap when needed.
The tech might spray a sample with DFO, bake it in the oven, then darken the room, and put on orange plastic glasses. Then side-light the sample with a 455nm light. The photo would be taken at that point.
Ninhydrin, the third chemical group in the list to be used if nothing has shown up yet, comes in several forms: acetone, zylene and Noveck. Ninhydrin reacts to another set of amino acids and likes warm, moist air. If a sample is being saved overnight for processing, it can be placed it in a ziplock bag, blown into, then sealed and still maintain its integrity.
Before working with any chemical, it’s a good idea to make copies of the document. Why are there different kinds of Ninhydrin? Zylene will run some inks. Acetone will run all inks, all the time. Ooops! There goes the document if you grab the wrong chemical, so copies are definitely necessary. Noveck is the clear winner when working with inks. It gets fast results and dries quickly. Additionally, it can be sprayed on an outer envelope to reveal what’s inside. Without damaging either piece of paper. Very cool.
Jake’s killer will never see the cash.
*Photos taken by Patti Phillips at Sirchie Education and Training facility in Youngsville, NC
For more information about Sirchie and its products for the law enforcement community, please visit www.Sirchie.com
I watched one of the CSI NY television episodes last Friday and was struck, yet again, by the Hollywood look of their crime labs. I like the show because of the actors and some of the cases, but as I’ve said before, TV sets and real life investigations bear little resemblance to each other – not in time, or equipment, or budgets. But, the viewing public expects the local police departments to have all that equipment readily available and is upset with the super long wait for results. It’s called the ‘CSI-effect’ and the guys and gals in real-life law enforcement have to deal with it all the time.
In the real world, investigators and examiners prove a case against the possible suspects using proper evidence collection techniques and tools, with hard work – not flash results in 50 minutes.
Fingerprints found at the scene are still the favored piece of evidence tying the suspect to the crime. These days, using a combination of ingenuity and newly developed chemicals and powders, a crime scene investigator can lift (and/or photograph) prints from many previously challenging surfaces.
After dusting for prints with black fingerprint powder,
they can be lifted from various smooth surfaces using (in forefront) a gel lifter, a hinge lifter and (in background) tape.
Prints are photographed and then can be viewed under an Optical Comparator. This machine can be hooked up to a laptop, and the image sent off to AFIS for ID.
We hope for a complete print, but the usual occurrence is that most of the time, partial prints are left at the scene. That’s what makes the search for the suspects so much tougher than what the TV dramas tell us. There is no instant ‘a-ha’ moment that comes right after the crime has been committed. In a real lab, AFIS comes back with a list of 10-20 possible matches and someone then makes a comparison by hand of the most likely hits.
Some things to keep in mind:
*A print can disappear over time and there are too many variables (temperature, humidity, condition of the surface, etc.) to predict how long that will take.
*A really crisp print can be photographed right at the scene, using some great digital cameras now available.
*Forensic science is not a certainty, even though TV shows may give that impression.
*There is no nationwide standard for number of points of ID for a fingerprint. In the year 2013, the acceptable number of matching points (between the actual print and the print in the AFIS database) can range from 5 to 20 depending on where the suspect lives.
There is no such thing as a perfect crime, but the jails are filled with crooks that swear they have been framed. One of my favorite excuses: “Somebody planted that print.”
That only happens on TV and in the movies.
*Photos taken by Patti Phillips at the Sirchie Education and Training Center, Youngsville, NC.
During our last trip to Ireland, Sheila and I had lunch in many different restaurants, in both big cities and small villages throughout the country. We were surprised to see that there were two comfort foods common to every mid-day menu: Brown Bread and Irish Peasant Soup. While I’m traveling, if I find something I like to eat, I tend to stick with it, just to be on the safe side. Sheila says I should be more adventurous, but IMO, odd sauces can cover up a LOT of mystery meat.
Having said that, we discovered that each of the places had different recipes for the soup. Sheila came up with this combination of vegetables after striking up a friendship with a chatty cook who revealed that the soups are basically created using whatever is fresh from the garden that week.