As many as 18 people broke into the post office at the Thompson Center in the Loop early Monday, according to Chicago police.
The group broke through the front door of the post office in the first block of West Randolph Street about 12:35 a.m., police said.
No one was in custody.
Although police reported 18 suspects, video shared Monday afternoon by the U.S. Postal Inspection Service shows about six or seven young males entering the post office.
The video shows them wandering around inside the office, some of them off camera, before they dashed out within 45 seconds of entering.
The first person to enter the post office is seen in the video holding a bag as he exits.
Police were still investigating what was taken, CPD spokesman Tom Ahern said in a text.
The post office will be closed until further notice, according to signs taped to its windows late Monday morning by a postal inspector.
The U.S. Postal Inspection Service said it is investigating the break-in with Chicago police.
“We are gathering information and will attempt to release information as warranted at a later date,” inspection service spokeswoman Mary T. Johnson said in an email to the Sun-Times.
She did not answer further questions about the number of suspects or what was taken.
Although it’s unclear what the group wanted to steal, thieves have been targeting Postal Service letter carriers for their master keys — also known as arrow keys — that can open all group mailboxes, such as those inside the lobbies of apartment buildings within a particular ZIP code.
Thieves have used those keys to steal mail and collect written checks, which can be washed of their ink and rewritten for themselves, the Sun-Times has reported.
Security at the Thompson Center is controlled by a development partnership that includes Michael Reschke, chairman of Prime Group, and Quintin Primo III, executive chairman of Capri Investment Group.
Primo said the incident appeared to be a “random act of violence.” He also said the partnership is working with law enforcement on the matter and is “committed to the safety and security of the Thompson Center.”
The building ultimately is to be owned by Google, which plans to occupy it in 2026.
Contributing: David Roeder