Defendants in at least 29 criminal cases were acquitted or had their sentences reduced over the past decade because they had dementia at the time of the incidents, the Mainichi Shimbun has learned.
In 12 of these cases, law enforcers failed to conduct psychiatric tests on the defendants at the stage of investigations.
The findings could call into question the way investigations and trials are conducted on elderly defendants as the number of people with dementia is increasing with the aging of the population.
Noting that some people with dementia tend to repeat offenses such as shoplifting because of their symptoms, experts said law enforcers and courts should cautiously judge whether defendants have dementia or whether their crimes were induced by the illness.
"There are many cases in which people impulsively commit shoplifting and other offenses because of the effects of dementia and suspicions remain over whether they can be held responsible for the offenses. I think many people have been arrested, indicted and convicted without the courts noticing they have dementia because some forms of the illness often remain unnoticed," said lawyer Daigo Hayashi, who is well versed in offenses by people with dementia.
"Law enforcement authorities and courts need to accurately judge whether defendants have dementia and whether and how far such conditions affected their offenses, and the national government should conduct a survey on the situation surrounding such incidents. Even if offenders with dementia are deemed to have the capacity to take responsibility for their crimes, their conditions could worsen if imprisoned. It's desirable for such offenders to undergo medication in their regional communities or receive counseling," he said.
There are no statistics on incidents involving people with dementia and their trials, according to the Justice Ministry.
The Mainichi Shimbun analyzed court rulings handed down between 2008 and 2017 on offenders suspected to have had dementia by referring to the database on court rulings on major incidents as well as interviewing lawyers and prosecutors.
The average age of the offenders in the 29 cases at the time of the incidents was 70. Of the 29 cases, 15 were thefts, eight were murders or attempted murders, three involved arson, and two others involved inflicting bodily injuries including a fatal case, while one was of indecent assault resulting in injury.
There were three confirmed cases involving offenders with dementia in each year between 2008 and 2012 but the number spiked to seven in 2015. The number remained at the same level the following year while six such incidents were confirmed in 2017.
Defendants in three of the cases, who had been accused of theft, were acquitted. In two of these incidents, courts concluded that the defendants were insane and unable to tell right from wrong or control their actions. In the other case, the court determined that the defendant did not intentionally commit theft.
In the 26 other incidents, defendants had their sentences reduced to suspended prison terms or fines because they had dementia at the time of the incidents. Courts judged that defendants in 14 of these cases had a diminished capacity to control their behavior and that their capacity to be held responsible for the incidents was limited. In the 12 other cases, courts judged the defendants had the capacity to take responsibility for their offenses but recognized that they were unable to control their impulses due to the effects of dementia.
Prosecutors conducted psychiatric tests on defendants in 15 cases before indicting them. Many of these cases involve serious offenses subject to lay-judge trials, including murder and arson.
Psychiatric tests were never conducted on defendants in 12 cases including theft before they were prosecuted, and there are suspicions that the effects of dementia on their offenses were overlooked. It remains unclear whether psychiatric tests were conducted on the defendants in the two remaining cases.
In 2016, the Justice Ministry released statistics showing that some 1,100 inmates aged 65 or over, who were serving prison terms, or 17 percent, may have dementia. The ratio was almost equal to that of dementia sufferers to all people aged at least 65.
A total of 125 elderly inmates have been diagnosed with dementia. Many other inmates are believed to be serving their prison terms without anybody noticing that they have dementia.