In a small provincial village, a four-year-old girl was snatched from her home during the night, taken to a nearby rice field and brutally raped.

Her mother found her in the morning with one eye swollen shut and a ragged wound on her throat where her attacker had tried to crush her windpipe. A family friend, who was known as an “uncle”, was suspected but wouldn’t confess.

The police called in the Child Protection Unit (CPU) and one of the detectives sprayed the suspect’s hands with luminol, a chemical used to detect traces of blood.

From under the man’s fingernails a tell-tale blue glow emerged. That forensic evidence would make all the difference, said James McCabe, the head of the CPU. “[The suspect] was charged and he will end up being convicted. What was a weak case is now very strong.”

McCabe said Cambodian police already used basic forensic techniques – such as taking fingerprints and footprints and crime scene photography – but the CPU was helping them take their craft to the next level.

The use of luminol was just one of the new techniques the CPU has introduced. Others included the creation of detailed crime scene diagrams and DNA collection.

This has helped the standard of investigation procedures improve in Cambodia’s countryside. “We’re seeing an enormous improvement,” said McCabe. “And it’s the CNP who are doing it. They have a real want to use new techniques and to work.”

Many provincial police officers had received training in advanced investigative techniques but due to a lack of resources had rarely been able to put them into practice before.

“Thanks to the CPU, we can solve cases much more quickly and more easily than before,” said Tith Bunna, a senior CNP officer and head of crime scene investigation.