Prosecutors plan psychiatric tests to see whether a 40-year-old man can be held criminally responsible for a stabbing spree that left five people dead on Awaji Island, Hyogo Prefecture, earlier this month, investigative sources said.

Tatsuhiko Hirano is under arrest on suspicion of killing three of the five, with police continuing their investigation into whether he can be charged with murdering the other two as well.

Hirano has so far remained silent about the March 9 melee other than to say he will talk about it in court, the sources said.

Prosecutors allege that before the stabbing spree Hirano repeatedly posted messages on the Internet defaming the victims, and that the meaningless stories he has been telling investigators have prompted them to seek the psychiatric tests, the sources said.