A man believed to be in his 20s frequently visited Nippon Television Network Corp. in Tokyo, asking to meet with an NTV newscaster and a teenage actress, both of whom later became targets of letter bombs, police sources said July 17.

Newscaster Yumi Ida, 39, was targeted with a letter bomb July 16. Actress Yumi Adachi, who starred in an NTV drama series, was sent a letter bomb three years ago.

Police are investigating to determine whether the intended recipients' letter bombs were sent from the same man, the sources said. The Metropolitan Police Department is analyzing the handwriting in both letters. Until recently, the man had been a regular visitor to the television network's head office where he insisted on meetings with Ida and Adachi. Because of his insistent behavior, he was once taken to nearby Kojimachi Police Station, the sources said.

The investigators believe the letter bomb that blew up July 16 was sent from one of 152 mail boxes within the jurisdiction of the Kanda Post Office, because a 300 yen stamp was posted based on an estimated weight of 250 grams, they said. Investigators said the powder used in the bomb was of relatively weak strength and may be the same type commonly used in fireworks.

The device exploded in NTV's viewer services department. Employee Masamichi Maeda, 52, sustained minor injuries to his head and thumb.