When defending Japan's use of the death penalty, the government always cites overwhelming public support for the policy, and the last survey in 2009 showed 86 percent backed the status quo.

But a major new study by an academic in Britain shows "serious flaws" in Tokyo's assertion that the death penalty is universally popular and should therefore be maintained.

Mai Sato, from Oxford University's Centre for Criminology, shows that views are much less entrenched than previously thought, particularly after people have been exposed to more information on the subject.