Men who allegedly robbed a Tokyo gold merchant of ¥384 million in the city of Fukuoka on Thursday may have known his activities ahead of time and thoroughly planned the heist, investigative sources said Friday.

On Thursday, a man from Tokyo's Adachi Ward told police that he was sprayed with something before the thieves took a money-filled bag from him in a parking lot across the street from a Mizuho Bank branch in the Tenjin district at around 12:25 p.m.

According to investigators, the man, a 29-year-old employee of a precious metals shop in Tokyo, said he traveled to Fukuoka Tuesday to buy gold and had informed the bank he would withdraw the money on Thursday. He reportedly said he had visited the city a number of times for business.