A 28-year-old man pleaded not guilty Tuesday at the start of his Nagasaki District Court lay-judge trial to charges that he killed the mother and grandmother of a woman he allegedly roughed up and stalked in 2011 in a case that cast police under a harsh spotlight for their apparent inaction.

The defense team for Gota Tsutsui, whom previous reports said had confessed to the Dec. 26, 2011, slayings of the woman's mother Mitsuko Yamashita, 56, and grandmother, Hisae, 77, said it will also challenge the defendant's competency to be held criminally liable. The counsel didn't elaborate.

Prosecutors argued that Tsutsui, who is from Mie Prefecture, had intended to break into the home of his victims and kill them. He had met the woman online and, before stalking her had subjected her to violence. She was living in Chiba Prefecture at the time.

Tsutsui was indicted in April last year for stabbing to death the woman's mother and grandmother and stealing the victims' wallets from their home in the city of Saikai, Nagasaki Prefecture.

He also stands accused of sending intimidating emails to eight people, including relatives of the woman, whose name has been withheld for reasons of privacy.

The slayings provoked a public outcry after it was learned that the woman and her father demanded that Chiba police take action but their complaint was put off and investigators took a pleasure trip before launching an investigation.

Earlier reports said other police forces, including Mie's, were also alerted.

A verdict is expected to be handed down in Tsutsui's trial on June 14.