KOBE -- A message written on a note found stuffed in the mouth of 11-year-old Jun Hase's severed head last week bears a resemblance to those written by the "Zodiac" killer, who terrorized the San Francisco area in the late 1960s, investigative sources said June 4.

The note features a plus drawn within a circle, the sources said. Whenever the Zodiac killer struck, police and media received notes bearing similar marks. Zodiac was never caught, and his killings spawned a number of copycat cases, most recently in New York City.

Police think that a sharp knife and a tool similar to a saw were used in decapitating Hase, and have learned that a man holding a black plastic bag was seen early on the morning the boy's head was discovered, sitting near a side gate about 150 meters north of the main gate, the sources said. A black passenger car was also seen in front of the main gate at about the same time, they said.

A truck driver delivering food around 5:00 a.m. that day told police he saw a man wearing a black sweat shirt and dark pants sitting under a tree near the gate. He had a black garbage bag round in appearance, according to the account.

Police have determined that the head was put at the gate a few minutes after 5:10 a.m. No fingerprints were found on the two sheets of paper with the cryptic messages, suggesting that the murderer wore gloves. Thermal paper used in word processors was used for the handwritten messages, some among which read: "This is the beginning of the game," and "Nothing makes me more excited than killing."