An accused serial arsonist who claimed to have caused nearly 100 fires in Osaka pleaded guilty Thursday to four arson and attempted arson fires in May in his first trial session before the Osaka District Court.

Masao Tabata, 40, used a lighter and cardboard to start a fire in the early morning of May 26 at a house in Nishinari Ward, according to the indictment. His lawyer said he had no intention of burning the house down.

Prosecutors have also charged Tabata with three counts of attempted arson in Abeno and Higashi-Sumiyoshi wards on the morning of May 29.

Tabata has only been charged with four offenses so far. Since January, several suspicious fires broke out in the southern part of the city of Osaka.

Prosecutors plan to charge Tabata with more counts in August.