U.S. agents used an experimental system to trace the explosives. The composition of these particles, placed in explosives for the purpose of tracing them to their manufacturers, can disclose where, by whom and when an explosive was manufactured. There are records which lead from the manufacturer to the retailer to the purchaser who has to sign something to buy them. In this case the explosives batch was traced to a small dealer who sold dynamite from his home. From there authorities were able to get the name of James L. McFillan.
Bombings usually take months before an arrest is made.