Locard's Principle states that "every contact leaves a trace", and therefore every time an exhibit is handled there is the possibility that two-way transfer (cross contamination) may occur. It is not possible to identify how any particular trace may have arisen, or how long it has been present. The implication for law enforcement agencies is that it is likely to be suggested in court that they themselves are the source of any material found.

The safest way to ensure the forensic integrity of an exhibit is not to touch it.

If it is necessary to touch an exhibit, precautions need to be taken to minimise the possibility of transferring material. This is a two way process; it is important to minimise the contamination of the exhibit from the officer involved, and it is also important to minimise the contamination of the officer from the exhibit. If an officer becomes contaminated, it is possible that material will be transferred to items subsequently touched.

Oversuits and shoes can also help minimise transfer.

It is one thing to say that gloves were worn; but another to prove it. Retaining gloves (or oversuits) as exhibits helps. These would then be available to the defence if required (although analysis after use is of questionable value since it is not possible to say whether they were contaminated to start with or whether they became contaminated through contact with the exhibit). Another way of helping to ensure that particular individuals were not a source of contamination is to ask them to handle a clean piece of paper prior to handling the exhibit. This paper can then be submitted as an exhibit to demonstrate cleanliness.

Remember that the purpose of wearing gloves is to isolate a particular item from the person. The same gloves should therefore not be used to handle another item.

Exhibits should be double bagged, preferably in plastic bags, with both sealed. Note that the use of plastic bags is not the preferred choice for certain other types of forensic analysis. If in doubt consult MSA or the FSS hotline. The use of two bags further distances an exhibit from other potential sources of contamination. It could also be argued that certain compounds are capable of passing through plastic, and thus, double bagging reduces the possibility of this happening.

If both bulk and trace exhibits are involved, it is our recommendation that trace exhibits should be handled before the bulk drugs. No-one will argue that a bulk drug was significantly altered by a trace, but the converse could certainly be argued. If at all possible, bulk drugs and exhibits to be analysed for traces should be handled by different individuals.

This is crucially important, as for any other type of exhibit. Additionally, cash exhibits have obvious security problems. Our policy is that cash exhibits are either under seal or under video surveillance at all times.

Inform the laboratory of any other information which may assist in interpretation. This may include circumstances of seizure and other background intelligence. Since MSA perform “target compound analysis” it is imperative that we are informed if less common drugs are suspected, otherwise we will not look for them! Information such as the size of the total seizure, or any special requests (drugs, fingerprints, DNA, intact wrappings) would be beneficial. We routinely analyse approximately one third of the number of banknotes in an exhibit. If the exhibit is a proportion of a larger seizure, then we need to analyse a greater proportion of the exhibit in order to be able to draw significant conclusions.

Exhibits for trace analysis should be submitted to the laboratory as soon as is possible (within weeks rather than months). This is because drugs traces, in particular heroin and cannabis, degrade rapidly over time, and this degradation is exacerbated by increased temperatures. If exhibits need to be stored for a period of time prior to submission, we would recommend that they are stored securely at low temperatures and away from other sources of drug contamination.

When making cash seizures, it is important to follow procedures to reduce cross contamination which would reduce the evidential value.

1)An inert covering should be placed on all surfaces with which the money comes into contact (foil is suitable). This is to prevent the money from coming into contact with surfaces that may be contaminated with drugs, for example, the custody desk at a Police Station, surfaces in a suspect's premises, etc. Foil is cheap and impervious to drugs. Once the exhibit has been examined, the foil should be wrapped around the money before it is bagged up. This is because the foil prevents drugs from "falling off" the banknotes and leaching out of the bag, and also prevents drugs from leaching into the bag.

2)Gloves should be worn when handling exhibits (not just cash, but any exhibits), and handling should be kept to a minimum to reduce the possible re-distribution of drugs particles. To this end, it is preferable if the cash is uncounted (although we realise that this is not always possible).

3)Weighing rather than counting can help give some indication as to whether part of an exhibit has been removed, but if counting is necessary, there are a number of steps to reduce cross contamination. First, if counting by hand, gloves should be worn, and a paper swab of the gloves taken before any handling takes place. At the same time, a piece of blank paper should also be taken, in order to show the paper is clean. Both of these control samples should be placed in bags and submitted for analysis. The gloves should also be bagged and submitted for analysis after counting to show any contamination on the gloves. Low levels of contamination on the gloves are often found and are consistent with contact with the banknotes. Counting machines can also be used to count the banknotes, but if this is the case, the counting machines should be submitted for analysis, and it would be advantageous if blank pieces of paper were run through the machine before counting, and submitted for analysis, to demonstrate any contamination of the counting machine prior to counting.

Document Reference : MSA4648JBL

Version No. 2

Date : 30/01/2004