Footwear marks are the second most common evidence type left at a crime scene.
The Forensic Science Service Lambeth has an online database that contains tread pattern and code identification gathered over the past 25 years, as one of its forensic scientists explains.
No two firearms are identical.
Unique marks on the internal surfaces of the firearm are transferred onto the cartridge and the bullet during firing.
These marks can provide enough information to allow them to be traced back to the firearm, as shown here by a scientist from LGC forensics in Leeds.
The generation of a DNA profile allows investigators to link an individual to a biological sample taken from a crime scene.
Sample sources can include blood, saliva, semen, hair, bone, faeces, urine, teeth and tissue.
