Photo/IllutrationDefense lawyers hold a news conference on Feb. 20 after the Tokyo District Court acquitted a male doctor accused of molesting his female patient after surgery. (Asahi Shimbun file photo)

Evidence presented at a criminal trial can prove the defendant's guilt beyond a reasonable doubt. But it can also exonerate someone who was falsely accused.

Yet, cases have surfaced of investigative authorities' incredible lack of understanding of this crucial fact.

The Tokyo District Court earlier this month acquitted a male doctor accused of molesting his female patient after surgery.

The presiding judge concluded that there was no denying the possibility that the patient could have experienced hallucinations due to delirium induced by anesthesia and post-op pain.

Even though an association of medical professionals had pointed out this possibility earlier, prosecutors proceeded to build their case around trace evidence, collected from the patient's body, from which the doctor's DNA was detected.

The trial brought to light the extreme sloppiness with which the evidence was handled.

The forensic science laboratory of the Tokyo Metropolitan Police Department was found to have been using lead pencils for recording evidence-appraisal procedures, so that corrections could be made later--which the institute actually did make--by erasing earlier entries.

As for DNA solutions left over from the tests, they could not be re-examined for accuracy because the laboratory had "discarded them during the annual cleaning."

Noting "the dubiousness of the examiners' sincerity," the presiding judge concluded that the test results could not be admitted as evidence of the defendant's guilt.

Simply put, what could have been crucial evidence in the prosecution's favor was discredited by none other than by this investigative organ.

But improper handling of evidential materials is nothing new. Attorneys have complained about investigators using up all collected samples during testing for no pressing reason, effectively rendering it impossible to retest them and disprove earlier results.

Since 2010, the National Police Agency has repeatedly issued directives on the careful maintenance of forensic records. But it is now clear that the directives have not been followed.

Amid recent advances in DNA testing technology, laws have been instituted in the United States and Europe to ensure proper maintenance of evidential materials and guarantee the rights of convicted defendants to seek re-examination of test results after their trials.

The Asahi Shimbun also has called for necessary legal amendments in its editorial.

Given ongoing developments around the world, as well as in light of the latest Tokyo District Court ruling on the doctor-patient molestation case, Japan needs to clarify and tighten its rules by law, not through government "directives."

A scandal that surfaced recently at Saitama prefectural police also cast light on police officers' unacceptably sloppy handling of evidence.

In a fatal hit-and-run case, the officers not only misplaced the wristwatch the victim--a young boy--was wearing, but are also under suspicion of retrieving its original list of evidential items from the boy's family and replacing it with a new list from which the wristwatch was deleted.

Problems concerning the handling of evidence are occurring all the time. Some local police stations are trying to remedy the situation by letting their headquarters centrally manage the items, rather than doing this themselves.

Still, tougher measures are needed to prevent a recurrence.

Japan's criminal investigators are now under growing pressure to end their overdependence on confessions. Also growing is the importance of "objective evidence" obtained from items left at the crime scene and from forensic examinations.

All investigators need to bear firmly in mind that shoddy handling of evidence is never to be condoned.

--The Asahi Shimbun, Feb. 25