Images of that gaping hole in the multi-story Murrah federal building in Oklahoma City, after Timothy McVeigh detonated a ton of ammonium nitrate fertilizer, which explodes, in the nearby street and killed 168 people are ingrained in America’s memory.

Now a report reveals that federal investigators are trying to figure out what happened to 30 tons of the same material that disappeared en route to California.

The Daily Mail reveals that the material “vanished” during a journey from Cheyenne, Wyoming, to Saltdale, California.

The report explained the material, in pellet form, was from a Dyno Nobel manufacturing site and left April 12. It was reported missing when the train arrived on May 10.

Union Pacific says it does not believe “criminal” activity was involved and some reports suggest it simply leaked from the rail car.

However, no one yet has explained what happened, or where is the explosive material now.

Using a box truck, McVeigh and Terry Nichols hauled about a ton of the material to the street in front of the Murrah building and detonated it on April 19, 1995. McVeigh later was executed.

An accident involving ammonium nitrate, at a fertilizer plant in Texas, killed 15 people in 2013.

And more than 200 died when thousands of tons exploded at the Port of Beirut in Lebanon.

Officials revealed the railcar was sealed when it left Cheyenne, and the seals were intact on arrival, but the surmise was that it leaked through a bottom gate in transit.

“Our investigation is still ongoing at this time. Union Pacific cannot comment on the details or status of an active investigation, other than to say that at this point in the investigation, we do not believe there is any criminal or malicious activity involved,” a railroad official said.

This article was originally published by the WND News Center.

This post originally appeared on WND News Center.