Photo/IllutrationYuji Hiroshige, senior researcher at the Aichi prefectural police crime laboratory (Tatsuro Sugiura)

  • Photo/Illustraion

NAGOYA--It's the classic midsummer night's whodunit murder mystery: A locked room, a corpse, a dead mosquito, no witnesses, and no obvious clues.

But Yuji Hiroshige, a senior researcher at the crime lab of the Nagoya prefectural police here, reckons such a case is eminently solvable.

Just extract the blood from the mosquito, run a DNA test and bingo, a match can be found--unless, of course, the insect bit the victim, not the perpetrator of the crime.

As Sherlock Holmes would say, "Elementary, my dear Watson."

Hiroshige, 37, sometimes wondered whether those bloodsuckers could provide answers when he found dead mosquitoes at murder scenes.

His research, which earned him a doctorate in medicine from Nagoya University, showed that human blood extracted from mosquitoes remains viable for DNA analysis for up to two days after a bite, enabling researchers to roughly determine when the mosquito made contact.

“I was able to carry out my study thanks to the support of people around me, despite overwhelming pressure,” said Hiroshige, who was so focused on his research that he studied after work, during his days off and sometimes carried out experiments through the night.

Hiroshige's job in the lab is to analyze DNA samples of evidence found at crime scenes. He joined the study at the university in autumn 2013.

The team examined DNA in blood extracted from two species of mosquito found in Japan: Asian tiger mosquitoes and culex pipiens pallens. The Research and Development Laboratory of mosquito coil maker Dainihon Jochugiku Co. helped the team by supplying mosquitoes for experiments.

A research kit for crime investigations was used to examine 15 DNA sequences in human blood collected from mosquitoes with the aim of finding a match.

The team found that a match could be made within 48 hours, based on all characteristic DNA patterns at 15 particular locations. Researchers were also able to roughly determine when the individuals were bitten with an incremental unit of 12 hours, based on the degree of decomposition of the DNA.

DNA degrades as the blood is digested in mosquitoes’ bodies.

However, sufficient amounts of DNA remain in the blood within 48 hours after the initial bite.

Kengo Ono, the laboratory's deputy director-general, said that to present a foolproof case, investigators would have to prove that a mosquito was present at a crime scene prior to an attack.

“We still have many challenges to overcome,” said Ono.

Yet, Ono is convinced that mosquitoes could tip the balance in a criminal case and provide significant evidence in proving "how long before and who was at a particular crime scene, especially when there is no surveillance camera footage or witnesses."

In the 1993 U.S. movie "Jurassic Park," scientists cloned dinosaurs from the DNA obtained from mosquitoes that had sucked blood from dinosaurs.

Hiroshige is committed to pursuing similar research, albeit not involving dinosaurs.

The study also inspired mystery novelist Yukito Ayatsuji, author of “Jukkakukan no Satsujin,” which has been translated into English as “The Decagon House Murders.”

“Mystery novels have been linked with state-of-the art science and technology since the good old days of Sherlock Holmes,” Ayatsuji noted, calling the study profoundly interesting even for novelists as DNA analysis is now an essential component of modern detective work.

“Different scenarios based on such a study come immediately to mind (in writing novels),” said Ayatsuji.

“For instance, I can depict the psychology of the perpetrator who has no choice but to use insecticide at the crime scene because he knows mosquitoes could be used as evidence.”

Ayatsuji said he also conceived a scene of mounting urgency as police search for a mosquito before the time limit for detecting DNA in the insect's blood runs out.

“Unfortunately, such scenarios cannot be used in my “Yakata” (house) series as those stories were set in 1990s,” he said.