OKINAWA CITY — Okinawa police are investigating the cause of a junkyard explosion that killed a 53-year-old Japan Air Self-Defense Force airman Sunday.

The 3:50 p.m. blast inside the first floor of the junkyard office may have occurred while Senior Master Sgt. Takio Tamura of Naha was cleaning discarded artillery shells in preparation for resale at local flea markets, police said. Tamura, stationed at Naha Air Base, was killed instantly.

The cause of the explosion has yet to be determined.

Police said they found 28 U.S. practice grenades in Tamura’s nearby van. A Japan Ground Self-Defense Force bomb disposal team concluded they did not contain explosives.

Each light blue shell measured about 3 inches by 1.5 inches, police said. It was not immediately clear where Tamura obtained them.

No other explosives were found, police said. But several other military-related items were found in the van and subsequent searches of Tamura’s home and office at Naha Air Base.

The items included cartridge belts, fuses, stabilizing fins for rockets and live cartridges, police said.

According to local news reports, the junkyard is owned by a man who sells shells, camouflage clothing and other military gear at a flea market booth he operates on weekends.

A Naha Air Base spokesman dismissed speculation Tamura had smuggled ammunition from the base. He said Tamura worked as a car mechanic and had no access to the base arsenal.

The owner of the junkyard was working on the second floor of the building when the explosion occurred, police said. He was not injured.

An autopsy performed Monday showed Tamura died from massive bleeding from multiple wounds, police said. Preliminary tests showed Tamura had been handling nitric acid.

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