The size of the bullet hole left in the skull of a murder victim varies according to the individual’s bone density, a new study has found.
Ann Ross: hopes new research
will help identify gun calibre
The findings are important as it is not always possible to receive bullets in such cases, meaning the calibre of the murder weapon can only be determined by examining the size of the entry wound.
They have emerged from a proof-of-concept study conducted by a team led by Dr Ann Ross, professor of biological sciences at North Carolina State University. Previous research by Dr Ross, a forensic anthropologist who has worked extensively on investigations throughout the United States and elsewhere in the world, had determined that skull thickness and bullet calibre could affect the size of the "minimum diameter" entry wound in a skull.
For the new study, Dr Ross evaluated the bone density of 18 skulls – all had been victims of gunshot wounds to the head – for which the bullet calibre was known.
“Based on this small sub-sample, we found that the strongest correlation was between bone density and minimum diameter size of the entry wound," said Dr Ross.
"The second highest correlation was between bullet calibre and minimum diameter size. That tells us that bone density is an important variable. We need to replicate this with a larger sample size, but it's clearly an important area for future work.”
The research team also found that bone density and skull thickness did not correlate. This is an important observation, because previous research – including Dr Ross's own work – had used skull thickness as a proxy for density.
Dr Ross also looked at minimum diameter wounds in a sample of 169 skulls for which they did not have bone density information. They found that, without that bone density information, minimum diameter size allowed them to estimate whether a bullet was small calibre (up to .32 calibre) or large calibre – but they were unable to be more specific.
"We're optimistic that, with additional research, we'll be able to use bone density and minimum diameter to provide much more accurate estimates of bullet calibre to the authorities," said Dr Ross.