(CNN) -- When 400 guns go missing, there's cause for concern -- understandably.
For two days, agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and local law enforcement searched for two men who stole that many weapons from a UPS facility in Memphis.
The burglary occurred Sunday. Officials say two men drove up in a U-Haul truck and made off with about 400 guns.
On Tuesday, the ATF's Chicago office said "hundreds of guns" stolen from the distribution center have been recovered in Illinois.
The office said it has one person in custody, but it's looking for a second.
CNN has reached out several times to the ATF for more details, and is waiting to hear back.
The prospect of stolen guns flooding Memphis had some residents worried.
"It's very scary, because we don't know what they might be able to do with that," one resident, Julio Rodriguez, told CNN affiliate WMC. "It's sad, man. But I feel like there has to be more security, you know?"
A UPS spokesman told CNN the company is working with law enforcement but can't comment on an open investigation.
Anyone with information can call ATF at 1-800-283-4867 or the Memphis Police Department at 901-528-2274 or email a tip to ATFTips@atf.gov