Foiling the perfect crime, with the help of a mozzie

This technique can help police work out who was at a crime scene. In the future, it might provide evidence that can be used to convict offenders.

Toshimichi Yamamoto

The murderer absconds with a smirk, knowing he has covered his tracks like a pro – no witnesses, no finger or footprints, no stray hairs to betray his identity.

But if a mosquito bit our cocky assassin at the crime scene, it could one day lead to a conviction, according to a study published on Monday in the journal PLOS ONE.

That is because researchers at Nagoya University have shown that human blood extracted from a buzzing bloodsucker can be traced back to its original owner up to 48 hours after a skeeter has siphoned it off.

“This technique can help police work out who was at a crime scene,” lead scientist Toshimichi Yamamoto said in a statement.

“In the future, it might provide evidence that can be used to convict offenders.”

No one knew how long human blood drawn by a mozzie kept an identifiable DNA profile, so Yamamoto and a team of forensic scientists decided to find out.

They recovered blood from mosquitos who had bitten volunteers, and then used a technique called polymerase chain reaction – PCR for short – to examine it.

PCR is a standard tool in forensics for amplifying a tiny DNA fragment up to thousands of times.

The researchers found that they could accurately match the minuscule blood traces to the volunteers who had offered themselves up as a meal, even after two days of digestion in a mosquito’s stomach.

After three days, however, the blood completely broke down.

The experiments were performed with two species, Culex pipiens pallens and Aedes albopictus, both found throughout much of the tropi- cal and sub-tropical world.

“We hope this will help crime scene investigators collect reliable evidence,” Yamamoto said.

With further research, he added, it might be possible to accurately estimate when a mosquito plunged his syringe into its victim.

Most mosquitoes do not travel beyond a radius of a few hundred metres and, depending on the species, have lifespans ranging from a few days to a couple of months.

Females – the ones that bite – generally live far longer than males. — AFP