California officials are investigating the disappearance of 30 tons (61,000 pounds) of ammonium nitrate from a railcar crossing the Midwest. Ammonium nitrate, which is used as fertilizer, can also be used to create explosives and was a key component in the homemade bomb used in the 1995 attack on the Murrah Federal Building in Oklahoma City.

The chemical was shipped by train from Cheyenne, Wyoming last month but when it arrived in the Mojave Desert two weeks later, its holding car was empty and the nitrate was gone. Dyno Nobel, the company responsible for shipping the ammonium nitrate is a leader in commercial explosives and filed a report with the federal National Response Center (NRC) on May 10 and an investigation is currently underway.

The Federal Railroad Administration, the California Public Utilities Commission, Union Pacific, and Dyno Nobel are looking into the disappearance, and the railcar is being transported back to Wyoming to undergo a thorough inspection.

It is unclear how or when the chemical disappeared during transit, but Dyno Nobel told KQED News, “The railcar was sealed when it left the Cheyenne facility, and the seals were still intact when it arrived in Saltdale. The initial assessment is that a leak through the bottom gate on the railcar may have developed in transit.”

Given that the chemical can be used to make highly explosive bombs, the loss of such an enormous amount of explosive material is highly concerning, and Stan Blake, a former Wyoming lawmaker and retired train conductor told Cowboy State Daily News it wouldn’t have been difficult to drain the train car of the material. Blake told the outlet that each car has two or three sections with a gate at the bottom, and said, “You can use up a big bar and open that gate and it’ll pour out.”