The Butler County Sheriff’s Office is coming up empty following a late Wednesday-night report of a possible active shooter in El Dorado.

Authorities say responding deputies were unable to find any sign of three men, one of whom reportedly appeared to be armed with an AK-47, at the HollyFrontier Refinery following the 10:30 p.m. call.

A department spokesperson says deputies, who were later joined by SWAT officers, spent about seven hours at the site. Refinery officials later issued a statement saying authorities had deemed the report “not credible.” The incident remains under investigation.