A Nihon Keizai Shimbun Inc. employee fired Tuesday after his arrest on suspicion of insider trading has told investigators that stock trading was his hobby and that he placed Internet orders from home and work -- sometimes at a rate of 100 or more per day -- sources said Wednesday.

Kazumasa Sasahara, 31, worked in the advertising section of the business daily's Tokyo head office. He was arrested Tuesday on suspicion of violating securities law by using confidential information obtained on the job to play the stock market. The newspaper, widely known as Nikkei, fired him later in the day.

According to the Nikkei, which started an internal investigation after suspicions arose in February, there were several instances in which Sasahara got advance notice of stock splits from legal notices scheduled to be published in the newspaper and started trading in companies he thought the information would affect.

Sasahara began trading stocks in March 2004 and had accounts at as many as 15 securities firms, the sources said. However, while Sasahara told police that his trading turned illegal last summer, the Securities and Exchange Surveillance Commission alleges he began insider trading between last December and January, the sources said.

The Tokyo District Public Prosecutor's Office is aware of that information but is being cautious as it is still not clear if he accessed the paper's internal computer network as alleged, the sources said.

Sasahara may have used advance information on stock splits from five listed companies, including a maker of children's clothing, that published legal notices via the daily's Osaka head office.

The securities watchdog alleges Sasahara made about 30 million yen off of 240 million yen' worth of trades involving about 94,000 shares in the five companies between Dec. 13 and Jan. 31.