A 28-year-old man pleaded guilty Thursday to killing four people in separate robberies last year during his opening trial session before the Nagano District Court.

Shojiro Nishimoto is charged with fatally stabbing taxi driver Yasuo Minato, 59, in Aichi Prefecture in January last year and killing three elderly people in separate robberies in Nagano Prefecture from April to September that year, stealing a total of about 300,000 yen from the four victims.

Communities in Nagano Prefecture were shaken last year by the killings of Jitsue Shimanaka, 77, Masashi Kato, 69, and Aiko Kimura, 74, who were either strangled or stabbed in their homes, where they lived alone.

Nishimoto also pleaded guilty to a separate case of theft in which he is accused of breaking into a man's home in Nagano Prefecture and stealing about 10 million yen in cash in September 2003.

He confessed to the killings after he was arrested in September on a different trespassing case. "I wasn't eating enough, and all I could think of was killing and robbing people," Nishimoto was previously quoted as telling investigators.