BFRO Tips for Collecting Evidence

Tips for Photographing and Measuring Tracks

The most common problem in studying photos of tracks is the in determining the actual dimensions of the tracks. When photographers do think to place something alongside a track to provide scale, they usually put their own booted foot next to it. While this may be better than nothing at all, it complicates independent analysis of the photos because, of course, not all shoes or hiking boots are the same size. The best way to facilitate analysis of photos of tracks is to place some common consumer item next to it, like a pop can, a pack of cigarettes, or anything you happen to have with you that is mass produced, in a consistent size and shape, and is widely available.

Individual tracks should be photographed in sequence, and from various angles. It's very important to also photograph the track pathway, showing several tracks in one frame with scale items placed near the tracks. This will make it easier to accurately measure the distance between tracks later. A track pathway should also be photographed from several angles, e.g. from directly above, looking down onto them; from the side, high enough so the tracks can be clearly seen; from the pathway itself, looking along the path from a standing height; etc.

When making track measurements, each footprint side (both prints from the left foot and prints from the right) should be measured for length and width. When measuring the stride or step length, (i.e. the distance between steps) the steps should be measured from the same point on one footprint to the SAME POINT ON THE NEXT FOOTPRINT. Very often people only measure the open space between foot prints, without noting their method in the measurement data, which leads to a substantial underreporting of step length.

Sections of full-sized footprints frequently include partial or seemingly half-footed imprints on the same trackway. These are important items with respect to foot anatomy and gait. These different types of foot prints should be documented in combination with the step length (heel to heel measurement).

Good height estimates combined with foot prints measured on the ground are extremely valuable. Additionally, grouped footprint tracks, such as those apparently made by an adult and infant, should be studied with great care to determine to what degree the infant is (intermittently) carried. Such occasions are, of course, extremely rare, but having thought through what to do in such a situation is half the battle.

Best Material for Making Casts of Tracks

"Ultracal 30" is one of the best materials for making casts of tracks. It's manufactured by U.S. Gypsum. You can find it in building supply stores that sell plaster supplies to building contractors.  "Ultracal 30" sets in 30 minutes.This casting plaster has almost no expansion or contraction when it sets. The cost is about $20.00 for a 100 lb bag.

Dental Stone is also a good choice, as it is stronger, and shows greater detail than Ultracal 30.  It is also, however, more expensive at around $30.00 for 25 lb bag.

If it can be found, Quik Roc is an excellent casting material.  It is strong and durable, and relatively cheap at $25.00 for 50 lbs.  Its best feature is that it dries in under 10 minutes.  It can be found at some building supply stores.

Another good choice is Hydrocal Gypsum Cement.

If at all possible, don't use Plaster of Paris. It crumbles quite easily.

Tips for Casting Impressions and Tracks

These tips are designed to assist the field investigator in casting impressions in soft material like soil, mud, or even snow. This information is a set of guidelines and accepted practices derived from the law enforcement community. Most of the techniques presented are the "standard" used by not only local area law enforcement, but also by Federal agencies like the FBI and Customs.

Steps:

  1. Preserve scene integrity. Secure the scene and make sure that you have little or no intrusion onto it. This includes other investigators and/or associates. Keep EVERYONE off the scene until you have finished.
  2. Evaluate the scene. What kind of soil is it? How much moisture is present? How deep are the prints? Which prints are clear and well-formed? The answers to these questions will affect your casting. Take your time and evaluate it--the print(s) isn't going anywhere. The only thing that should press you for time when casting is inclimate weather. Rain can and will ruin an impression. If it is raining, cover the prints, and, if  possible, dig drainage trenches to keep water from flooding the print.
  3. Measure your scene and do a sketch. Take measurements of each print and the distance between steps. Also, measure the stride. Stride length is the distance from a particular point on one print to the SAME point where the SAME foot strikes the ground again. (i.e., right foot to right foot) Put all of these measurements on the sketch. The sketch doesn't have to be to scale, but the measurements have to be acurate. With acurate measurements, you can recreate the scene at a later date and different location.
  4. Select the print(s) you intend to cast. It is best to cast a row of prints.  In mixing the casting material, pour the water directly into a Ziploc bag or bucket and mix or knead the mixture. Make sure the mixture is consistent. You can adjust consistency to accommodate the conditions. If the soil is dry, the print detail will likely be more fragile. Without moisture to hold the soil together, the weight of the casting material may crush or damage the detail. In that case, you would want to make the mix more watery. This will make it easier to pour and more likely to fill in small cracks and crevices. If in doubt, err on the side of mixing it thinner. It takes a few minutes longer to dry, but the wait is worth it. If the print is unusually large, or if you doubt the strength of the cast, use some sticks or bits of wire to reinforce it. Lay it like you would lay rebar in concrete.
  5. Allow the print to completely dry, then lift it. For dental stone, it can take upwards of forty five minutes to dry--less in some cases, more in others. In almost all cases, the castings will be finished and dry enough to lift within thirty minutes. Allow more time for larger casts. When the cast(s) have dried to a medium consistency, you should take a knife blade or something similar and write your basic information in the back of the print. Include the date, time, and location at minimum. Put the corresponding number from you sketch onto the correct cast. For example, in your sketch you might have print 1, print 2, etc. Label each print as such. It is important to know where the print came from, and in which order they occurred in the trackway. Don't rely on use of a permanent marker for capturing this information on the cast. NO marker is permanent. Writing in the casting material will ensure that the information will remain intact. After marking the cast, allow it to dry until it is hard to the touch, and a blade will not readily pierce or mar it. Carefully take a shovel or other digging tool and go in a circle around the whole print. If you use a shovel, sink the blade to its entire depth in a circle around the print at a distance of no closer then about six inches. When your circle is complete, lift the print with the blade, carefully prying up. As soon as you can lift the cast by hand, do so. Knock the loose dirt off of it, and allow the print to dry for a day or two. At that time, you can use some running water to clean the cast completely.

Tips for Collecting Physical Evidence

Hair is best collected immediately into a small Ziploc baggie and sealed. Tissue or blood should be deep frozen immediately, preferably kept on dry ice. This is essential and helps keep the bacterial count to a minimum. Otherwise, the bacterial decomposition and bacterial DNA will swamp any possibility of extracting native DNA. Human contact should be avoided since even one or a few scales from the skin can compromise the results. Keep careful track of the chain of custody of your sample--the chain of people who have handled it and when.

There have been several occasions when people found half eaten apples or potatoes with conspicuous tooth marks in them and didn't bother to collect them. Many people don't realize the implications of seemingly trivial tidbits of evidence. The safest blanket recommendation for oddball organic evidence would be to deep freeze it and worry about its disposition later. It can always be shipped frozen on dry ice, if need be. The same would apply to skin and blood if present in any amount, though hair only needs a ziploc baggie.  

Camping Equipment Dealers and Expedition Outfitters

Recommended Outdoor Audio & Video Recording Equipment

When shopping for more common devices such as VCRs, walkie-talkies, etc., be sure to check the prices at Radio Shack. Tempting as it is to chuckle at the suggestion, Radio Shack is among the best sources for field equipment due to their liberal return policy available as part of their "extended warranty." This effectively becomes an insurance policy against any potential field damage. The other nice aspect to such purchases at Radio Shack is that you can walk into any local Radio Shack store (which are located all over the place) with your damaged unit and swap it for a new one right on the spot. Some have even been known to have swapped a Radio Shack VCR that was full of mud for a brand new one of the same type, over the counter and with no hassles.


 
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