This field consists of three different phases in which the experts work:
- Initial examination and documentation phase
- Bloodstain classification and investigative reporting phase
- Evaluative reporting phase
NRGD-registered BPA experts have been assessed on and have been found competent in all three phases.
Initial examination and documentation phase
During this phase, the expert documents where bloodstains are located. The expert also uses presumptive tests to determine if the stains are likely blood. This phase focuses on factually reporting the observations.
Bloodstain classification and investigative reporting phase
In this phase of the investigation, the expert performs the classic BPA tasks. These tasks are:
- Classifying and identifying bloodstain patterns
- Determining the locations, orientations, and movements of blood sources
- Determining the sequence of events
- Determining the minimum number of impacts
During this phase, the expert may offer a possible explanation of how the bloodstains were formed, within the context of scenario formation.
Evaluative reporting phase
During this phase, the expert investigates further what happened. The expert compares multiple scenarios and/or hypotheses and evaluates to which of these scenarios or hypotheses the patterns fit best and to what degree. For this, the expert can use Bayesian statistics, assign probabilities to findings, and provide a likelihood ratio in numerical and/or verbal terms.
Additionally, the following fields of expertise (as described by the NRGD), among others, fall outside of the field of BPA but the conclusions from these fields might be incorporated into a BPA report:
- Forensic Medicine
- Forensic Pathology
- DNA analysis and interpretation
- Weapons and Ammunition
- Gunshot residue
Any use of conclusions from other forensic, investigative, or medical reports, in the BPA experts report are to be considered summary statements only with the full conclusions and their context contained within referenced report.