The role of science in missing person searches in water
Sergeant Lorna Dennison-Wilkins joined the Sussex Police specialist search unit in 2007, the first woman on the unit since it was formed in 1966. Part of her role as a police diver and police search adviser, was to search for, and recover, missing people in hazardous places where additional personal protective equipment and skill sets were required.
When someone enters the water, there is a 90-minute survivability window1, so it’s imperative that an area search is actioned immediately. After this time, the search is classed as a recovery operation. If the individual is deceased, then there is often a window of time during which the chances of finding the body is much greater, once past that time period – which differs based on individual case factors – the probability of discovering the body decreases significantly.
During her work on the search unit, Lorna noticed that information about how human bodies move in an aquatic environment was limited. She was driven to further this field of knowledge after seeing first-hand the impact on families of not knowing the whereabouts of a missing person. Her personal commitment from being part of searches where family members would come to watch the search and wait for their loved one to be returned to them, means that she works tirelessly to help, even when on holiday.
Lorna notes, “I had seen the impact that not knowing the whereabouts of a missing person has on families and loved ones, and I wanted to do anything I could to alleviate
this suffering”.
During her first year on the unit, Lorna recognised that there were patterns in body movement in water2. However, there was no dataset or past research to refer to when making decisions, in terms of where in the water that person or body might be. Search teams should consider a myriad of variables when looking for a body in waters such as friction on the bottom of an area of water or snagging which keeps the body in one place, types and amounts of clothing, age and gender of subject, temperature, depth of water and the length of time submerged.
This gap in knowledge led Lorna to begin a study looking at patterns of body movement in water5, which involves the collection and analysis of quantitative and qualitative data relating to deceased human bodies found in inland water and experimentation to explore relationships between variables found within this field data.
In January 2021 she was awarded her PhD at the Leverhulme Research Centre for Forensic Science at the University of Dundee for research that built on her experiences of body recoveries in water on the Police Specialist Search Unit. Her research provides invaluable scientific insights for use by practitioners.
One of the key points that came out of Lorna’s research was that there are some strong principles which can help search teams to establish the buoyancy of a dead missing person and tailor it to the water environment. There are differences in buoyancy relating to the amount, type and construction of clothing and footwear; the fact that buoyancy increases with age of the individual; and the fact that the buoyancy of bodies differs depending on the manner of death. Factors such as heavy shoes can affect buoyancy, for example, no footwear or wearing boots seem to reduce buoyancy, while trainers and shoes aide it. Age is also an identified variable: in the initial phase (the first 24 hours), the older the body is, the more buoyant it is. This is likely due to reduced bone density, reduced muscle mass, increased fat and the impact of clothing and footwear.
The movement of a positively buoyant body will be influenced by the environment, such as the wind, water currents or flow. If the missing person is not located in the initial phase and is negatively buoyant, the search advisor will want to know if that body will come back up to the surface, and if so how long that might take.
A positively buoyant body which is free to move will be influenced by water dynamics, and if on the surface, by wind or other factors.
A negatively buoyant body can also be affected by water currents but this movement may be slowed by friction with the bottom of the water course and any obstacles it encounters.2
There are differences in buoyancy relating to the amount, type and construction of clothing and footwear.
The more layers of clothing worn, the more buoyant individuals are in the first 24 hours of the post mortem submersion interval. This was apparent in the field data analysis and during laboratory experimentation.4
| Clothing weight | Weight required to submerge models compared to no clothing (%) |
|---|---|
| Light | 50% |
| Medium | 300% |
| Heavy | 766% |
*For weights of clothing visit: https://doi.org/10.1093/police/paad037
In the initial phase (the first 24 hours):
Policing is increasingly an information-rich practice where effective knowledge sharing within and between police organisations is essential for success.
However, there is a critical conversation to have about how the service is going to get better at capturing and retaining expertise. There is a risk that, as experts retire, their knowledge leaves the force and there is a gap in skills and legacy that the next person in role does not yet have.
To help bridge any gaps, Lorna is passionate about passing down her knowledge to ensure that the extensive expertise she has gained is not lost. She hopes to help address the issue through the creation of an app that can assist search practitioners in identifying priority search areas based on the probability of buoyancy. “I did my academic research so that I could create something for practitioners. That’s always been my aim, to pay something forward for the search community.”
The aim of the app will be to capture all the analysis Lorna has completed for her PhD and the post-doctoral research that she has done since then. At any given time, a search practitioner or investigator can plug in the details of their missing person and get a probability of buoyancy that can then be tailored to the environment they are working within.
Lorna explains, “The information on the app will help identify priority search areas with consideration to the hypothesis the search adviser has formed. For example, if the person had fallen in by accident, if there was a swimming accident or if they’ve gone in to end their life, there would be different factors involved. These include the clothing and footwear worn and the manner of death and they would potentially change where that body might be. The app would take all those factors into account and assist the search team to target their search areas more effectively.”
Lorna is looking for funding to develop this app and is aiming for it to hold a real-time version of the models of prediction which are the results of her research. These models will be updated periodically as more cases are added to the database. It will incorporate the existing research and any wider research that could be relevant to the prioritisation of search areas and selection of resources in a missing person investigation.
Lorna is determined to ensure her expertise and knowledge are not lost “I feel a sense of responsibility to translate the findings of my research in an appropriate way and I feel strongly that we should value the application of science and the knowledge and experience of the search practitioner.”
