14.3: Bloodstain collection

Swabbing a suspected bloodstain is the easiest way to collect samples from large or immobile objects. If the stain is still wet, the swab can be dabbed into the stain until the blood is absorbed into the tip of the swab. Your author will avoid swabbing all the way to the target, instead focusing on collecting just the blood and not a potentially contaminated surface. Remember, you only need a small amount of blood for DNA testing. Wet blood should never be frozen; it is always best to place it in refrigerated evidence storage. Never store blood, whether wet or dry, in a plastic evidence container. Always use a paper bag or paper evidence envelope. If the stain is dry, moisten a sterile cotton swab with distilled water from an ampoule; avid using saline. Do not touch the ampoule to the swab, or the stain. Instead drop the water onto the swab or stain from a distance of about ½ of an inch. Touching the ampoule could cause contamination of both the swab and the ampoule. With the moistened swab, dab the stain until the swab contains blood. Remember to collect the blood specimen from the area between the center, which is clotted blood, and the edge, which may be serum. When collecting dried blood, you may have to scrub down to the target. It is unfortunately unavoidable. It is important not to place more than one sample into an evidence envelope and never collect multiple stains on the same swab. If you collected several swabs from the same stain, be sure to label each swab as coming from the same stain. Take a control sample in the same manner as the specimen from the area surrounding the stain without actually collecting blood or DNA evidence should your agency protocols require the collection of control samples. If sufficient sample remains, collect a dry-swab specimen as well. This swab is collected in the same manner as the specimen without using distilled water to moisten the swab. This specimen is generally retained for use by the defense.

Dried flaked blood

Blood that is dried and flaky can still have DNA value. The best method for collecting dried blood is to scrape it into a pharmaceutical fold or coin envelope using a sterile razor blade; or by picking up large flakes with sterilized tweezers. Be absolutely certain to wear safety glasses and a mask whenever manipulating dried blood as the last thing you want to do is flick a flake into your eye or mouth.

Processing wet bloodstained items

Many a seasoned detective or crime scene technician will remember processing wet bloodstained garments in open ‘drying cages’ overnight before carefully folding them up and placing them in paper bags the next day. That was in the days before DNA typing. Today, it is absolutely essential that agency evidence processing areas have contamination-free drying cabinets that use filters to purify circulating air. These cabinets must be lockable and have the means to clean and sterilize between each use and a logbook must be maintained to document the cleaning and sterilization process. These cabinets can be very expensive but are well worth the cost and are one of the most important acquisitions any law enforcement agency can make.

An item of evidence that is thoroughly wet with blood or other human biological evidence can be transported from the crime scene to the evidence processing area in plastic bags. It is best to put only one item of evidence in each bag. The items should only remain in the bag from the time that they have been collected to the time that they arrive at the processing area. The item should then be immediately transferred to the drying cabinet. The plastic bags and any paper placed underneath the item as it was drying also need to be dried and processed as they may contain trace evidence that may have fallen off the original item. Once the item has been dried, it needs to be properly packaged and processed in an evidence locker.

Items that are only slightly wet may not need to be cabinet-dried and may complete the drying process while in an appropriate non-plastic evidence container. Should this be the case, it is best to follow the package instructions listed below.

Bloodied evidence not at the scene

Bloodstained items of evidence often times do not remain at the crime scene. They are instead transported to vehicles or hospitals while the victims or suspects are still wearing them. Although every effort should be made to collect these items before they leave the crime scene, sometimes it is an unavoidable consequence of necessity. It is critical that these items are collected as soon as possible and that proper chain of custody is maintained by those individuals who did the collection. During a recent homicide investigation, your author needed a crucial piece of evidence: the shoes worn by the victim. After three days of searching, he finally found them in a cabinet at the hospital where the victim was taken and pronounced dead. As you can imagine, there was no chain of custody for the shoes. Regardless, your author collected them and processed them into evidence. They provided valuable information in the subsequent bloodstain pattern analysis and ownership of the shoes was confirmed through DNA typing.

As mentioned, you must never process wet, bloodied items in plastic. This can cause mold to grow that will degrade the DNA. Plastic should only be used to transport items to prevent cross-contamination.

Remember that the best short and long-term storage for liquid blood (such as that collected from a suspect or victim in a vial) is refrigeration. Never freeze liquid blood. Dried human biological evidence is best stored in a temperature-controlled storage area; however, room temperature is acceptable for short-term storage. The same applies to buccal swab samples.