The offender who robbed a man on a CTA train Sunday, Oct. 1. Police are seeking assistance in identifying the offender. (Photo taken from CTA security video)

Chicago Police Department mass transit detectives are seeking the public’s assistance in identifying a man responsible for an armed robbery on a CTA train.

Police said the robbery happened shortly before 8:15 a.m. Sunday, Oct. 1 at the Red Line Monroe Street station on the first block of South State Street in the Loop.

A man approached the victim and asked to use his cell phone. When the victim refused, the offender brandished a weapon and took the victim’s phone from his hand while also threatening him.

Police said the offender then got off the train at Monroe Street.

The offender was described as a Black man between 25 and 40 years old.

Anyone with information about the incident or offender should contact the Bureau of Detectives for Area Central at 312-745-4706.