DNA Science

Examination

Overview

Examination is the point at which exhibits and their case files are received from sample reception. The overall aim of examination is to firstly check the work of the SOCO and sample reception through a thorough administrative check, and secondly to obtain cellular material through a comprehensive examination of the item.

Administrative Checks

As mentioned above, the exhibit will be received along with its case file. This should contain all appropriate case details and a photocopy of the item as it was received. The contents of the case file must be checked against both the examination form and the item before each examination to ensure continuity between them. If an error is found on the examination sheet, then Sample Reception can correct it. However, if there is a query with the submission form or item then the SOCO involved must be contacted to rectify the problem before proceeding any further.

Examining Items

The first role of the examination is to make a detailed record of the item on the examination form. This will note the packaging and seals, along with a detailed description indicating the nature of the item, its condition and any labelling present. The second role is to obtain cellular material in an extractable form from the item. This may involve swabbing items and putting them into eppendorf tubes or cutting up larger items and putting them into universal or bijou tubes. After completion, a second examiner will repeat the administrative check and go through the examination form to ensure that it has been filled in correctly with the necessary sections signed and also to check that the sample has been labelled correctly.

How to determine what to examine

Often, police forces will submit multiple items for each case without specifying which items are to be examined. There are a number of factors to consider when deciding what to examine. Items found, or swabs taken from the interior of a property/car hold more value in court than those taken from outside, and therefore it is important to prioritise these first. Some items give higher success rates than others, for example cigarettes and blood stains are more likely to yield results than touch swabs and items put into universals. Therefore, it is more worthwhile to examine a cigarette before a screwdriver for example, unless stated otherwise by the police force.

Items unsuitable for profiling

Some items will be unsuitable for profiling, for example apparent bloodstains for which the presumptive test for blood has produced a negative result. Despite the fact that these samples will not be going any further through the process, they require examining regardless, clearly stating that the item is unsuitable for profiling on the examination form.

Sub-items

It may be necessary to create sub-items for some cases. This is used when multiple items have been submitted under one item number, but the police force has requested them to be profiled individually. This is often the case with cigarette submissions for example. Other circumstances that require sub-items to be created are when some of the item remains after the examination, leaving an opportunity to go back for further testing if necessary. A common example of this is with blood stained items where there may be numerous areas of staining, and only one area is taken for profiling.

Swabbing items

Items are to be swabbed firmly using wet and dry swabs. A swab dipped in fresh MilliQ water is used first, followed by a dry swab. This works on the principle that the wet swab will dampen the stained area allowing the dry swab to absorb the stain more efficiently. The areas swabbed are determined by what the item is and how it would have been used. For example, wet and dry swabs are taken of the area around the mouthpiece when swabbing a can, or around the handle when swabbing a tool.

Complex

Larger items such as clothing and airbags require complex examination. These items are examined in a detailed manner using an oblique light source. Items are tape lifted to collect cellular material or hairs. In some cases sections of the item may need to be removed and submitted. These submissions are dependent on how the exhibit was worn or used. Bloodstains are primarily submitted on a swab or as a section removed from the item.

Fingerprints

Sometimes items are submitted that require preserving for fingerprint analysis. In this case, the necessary precautions are taken so as to not to add further fingerprints or disturb any existing ones. However, on occasions a police force may submit an item that they would like preserved for fingerprint analysis, but due to the process we use, may not be possible. For example, latex gloves cannot be preserved, since it is the fingers that we use for our analysis. In this case the SOCO must be contacted to allow them to make the decision.

Photographs

Photographs with scales are taken of all items, excluding swabs, cig ends and sometimes hairs. Whilst used for continuity, these photographs add detail to the examination description and allow the scientist to highlight more accurately the areas swabbed or submitted for profiling.