1.1: Protection of Crime Scene

• A crime scene investigation begins with the initial response to a scene.

• Securing and protecting the scene are important steps in a crime scene investigation and this task is usually carried out by the first responding officer arriving on the scene.

• The entry of authorized personnel admitted to the scene should be documented using a log sheet.

• Suspects, witnesses, and living victims should be evacuated from the scene.

• If a victim is wounded, medical attention should be sought.

• Investigators should use proper equipment to avoid evidence contamination.

• Use a face mask or shield, safety eyeglasses, a disposable cover-all bodysuit, gloves, shoe covers, and a hairnet.

• Exposure to bodily fluids may occur during a crime scene investigation.

• Mucous membranes, skin, and needlestick injuries expose investigators to bodily fluids.

• Biosafety protocols protect workers from blood-borne pathogens.

1.2: Recognition of Biological Evidence

• A preliminary survey should be carried out to evaluate potential evidence.

• The recognition of evidence plays a critical role in solving or prosecuting crimes.

• Crime scene evidence should be prioritized by its relevance to the case.

  • Higher priority should be assigned to evidence with probative value to the case.

• Corpus Delicti: Refers to the principle that in order for an individual to be convicted, it is necessary to prove the occurrence of the crime.

  • In forensic investigation, it also refers to the physical evidence proving that a crime was committed.

• Higher priority should also be attached to evidence that can establish connections such as victim-to-perpetrator linkage.

• Locard Exchange Principle: Theorizes that the cross-transfer of evidence occurs when a perpetrator has any physical contact with an object or another person.

• Trace evidence, such as hairs and fibers, may be transferred from a perpetrator to a victim or vice versa. This explains why it is important to ensure that perpetrators and their belongings are thoroughly searched for trace evidence.

• Victim-to-scene and perpetrator-to-scene linkages can also be established.

• Blood belonging to a perpetrator or a victim found at a crime scene can establish such a linkage.

• Reciprocal transfers of trace evidence from crime scenes can be used to link a suspect or a victim to a crime scene.

• Modus Operandi: Refers to a particular pattern of characteristics and the manner in which a crime is committed.

1.3: Searches

• Some investigations require a search for specific items of evidence such as biological stains, human remains, and all relevant evidence.

• Search patterns may include a grid, line, or zone.

• The points of entry and exit and the paths followed by a perpetrator should also be searched.

• Searching for biological stains usually utilizes devices such as an alternate light source (ALS).

  • Alternate Light Source (ALS): Either produce a single specific wavelength of light or a desired wavelength by using specific filters.

• Biological materials such as blood, semen, and saliva emit fluorescent light under an ALS, which can facilitate the locating of biological materials.

• An electrostatic dust print lifting device can be utilized for processing impression evidence such as footprints and tire tracks.

• A high-intensity light-emitting diode (LED) device for locating evidence at a crime scene is particularly effective in highlighting trace evidence such as hairs, fibers, and shoe prints.

• Ground-Penetrating Radar: Uses electromagnetic waves emitted from a transmitter, which are detected by a receiver to locate clandestine burials and buried objects such as weapons embedded in soils.

• A tracking dog, such as a bloodhound, can potentially follow the scent from items left at the scene to locate a suspect nearby.

• Field tests and enhancement reagents can be used to facilitate crime scene searching.

  • These reagents can detect and identify biological evidence. The tests are very simple, rapid, and sensitive, and can be used at crime scenes.

• Enhancement reagents such as luminol and fluorescein, which emit chem-illuminant and fluorescent light upon reacting with certain biological materials, respectively, can be used.

  • It can also detect faint blood-containing pattern evidence.

  • Precaution should be taken since these reagents are not usually very specific to blood.

• Portable and field-deployable instruments have been developed that are capable of processing buccal swabs and potentially other evidence to produce a DNA profile on-site.

  • It is a fully automated process, using Rapid DNA technology that can be completed within 2 hours by a trained crime scene investigator or police officer.

  • This technology can enable law enforcement agents to rapidly determine whether the crimes were isolated incidents or part of serial crimes committed by the same offender.

  • It can also be used in the identification of human remains in mass disasters.

1.4: Documentation

• The conditions at a crime scene must be documented to provide vital information for investigators and for the courts.

• The most common documentation methods are drawing sketches and taking photographs and videos.

• The sketch is to reflect the positions and the spatial relationships of items and persons with measurements using a scale.

  • The investigator prepares a rough sketch first and turns it into a finished sketch after.

• If bloodstains are present at the scene, the location of bloodstain patterns should be emphasized.

• Photographs should include an overall scene view, a medium-range view showing item positions and relationships, and a close-up view showing evidence details.

  • Scales: Used to accurately depict the sizes of items such as bloodstains or bite marks.

  • Log Sheet: Used to record the chronological order of crime scene photographs and to note filming conditions and any additional relevant information.

• Written or audio-recorded notes can be used.

  • Notes should include complete and accurate information of a crime scene investigation, such as the case identifier number, the identities of the investigators, and a description of the scene or items.

1.5: Chain of Custody

• Custody information should be recorded at each event when evidence is handled or transferred by authorized personnel.

• A custody form listing a specific evidence item is used to document the chain.

• Each individual who acquires custody of the evidence must sign a chain of custody document.

• An incomplete chain of custody may lead to an inference of possible tampering or contamination of evidence.

  • The evidence may not be admissible in court.

1.6: Collection of Biological Evidence

• After the crime scene documentation is completed, the collection of evidence can be initiated.

• Small or portable items, such as bloodstained knives, can be collected and submitted to a crime laboratory.

• Large or unmovable items of evidence can be collected and submitted in sections, such as a section of the wall where bloodstains are located.

• Specific care is required for the collection of biological evidence in the following situations:

  • Bloodstain pattern evidence

  • Multiple analyses of the evidence

  • Trace evidence

  • Control samples

  • Size of stain

  • Wet evidence

1.7: Marking Evidence

• The marking of evidence is necessary for identification purposes so that it can be quickly recognized even years later.

• An investigator’s initials, the item number, and the case number are usually included in marking.

• Information can be marked on a tag, a label attached to the item, or directly on garment evidence.

• The marking of evidence should not be proximal to bullet holes or biological stains to prevent the mark from interfering with analyses.

1.8: Packaging and Transportation

• Packaging is intended to protect and preserve evidence.

• All evidence should be secured and protected from possible contamination.

• Fragile items should be protected to prevent any damage during transportation.

• Exposure to heat and humidity should be avoided to protect biological evidence from degradation during transport.

• Packaged evidence should be properly labeled with a description of the evidence and sealed with evidence tape.

• A seal should not be cut when a sealed evidence bag is opened.

• After the analysis is complete, the evidence packaging should be resealed.

Packaging of Evidence Methods

• Evidence from different sources

  • To prevent the transfer of evidence from different sources, items of evidence should not be grouped in a single package.

  • Items should be sorted depending on what type is it.

• Folding of evidence

  • Folding of clothing, especially items with wet bloodstains, can transfer evidence from one part of a garment to another.

  • If a large, dry garment must be folded, a piece of clean paper should be placed between different parts of the garment to avoid direct contact between the different parts of the garment, thereby preventing the transfer of evidence.

• Packing materials

  • Envelopes, bags, and boxes that are made of porous materials such as paper are appropriate for packaging dry biological evidence.

  • Dry, bloodstained evidence should not be sealed in plastic bags or containers that trap moisture.

• Liquid evidence

  • Tubes containing liquid such as blood should not be frozen because the volume of a liquid expands in freezing temperatures and this expansion may lead to cracking.

  • Tubes should be placed in plastic bags to prevent leaks in case of accidental breakage.

  • Liquid evidence should be transported and submitted to a laboratory as soon as possible after the collection of evidence.

• Trace evidence

  • All such evidence should be wrapped in paper with a druggist’s fold.

  • The wrapped trace evidence can be packed in an envelope.

1.9: Final Survey and the Release of the Crime Scene

• During a final survey, a discussion with all personnel in the crime scene investigation team should be carried out to thoroughly review all aspects of the search.

• It is important to ensure that the scene has been searched correctly and completely, and that no area has been missed or overlooked.

• All documentation including the chain of custody document must be complete and all evidence should be collected, packed, documented, and marked.

• Photographs of the final condition of the scene should be taken.

• Once the final survey is completed, the crime scene can be released.

• Reentry into the crime scene may require a search warrant after the scene is released.

• Crime scene release documentation usually includes the time and date of release, to whom it is released, and by whom it is released.

1.10: Crime Scene Reconstruction

• Crime scene reconstruction: The scientific process of determining the sequence of events and actions that occurred prior to, during, and after a crime.

• Process of Reconstruction:

  • Question Formulation

  • Information Collection

  • Hypothesis Construction

  • Prediction Making

  • Reconstruction Testing

  • Data Analysis and Drawing Conclusions

  • Theory Developing and Case Solving