The assailant in a knife attack in Kawasaki last week may have scouted the scene four days before he went on the stabbing rampage that left two dead and more than a dozen others injured, investigative sources said Monday.

Images of a man who appears to be Ryuichi Iwasaki, 51, were captured on the morning of May 24 by security cameras installed around the crime scene, as well as at nearby Noborito Station and Yomiurilandmae Station on the Odakyu Line, which is the closest station to his home in the city's Asao Ward, the sources said.

Police also discovered that Iwasaki bought the 30-centimeter-long knives used in the attack from a mass merchandise retailer in Machida, Tokyo, in February, so they suspect the crime was planned some time earlier.