Police shot the intruder, 47-year-old Donald Patrick, during SWAT unit active shooter training inside a Homan Square CPD facility at about 11:30 a.m., Supt. David Brown said during a Monday press conference.
Patrick allegedly asked to get property back at the facility at Homan Avenue and Fillmore Street, Brown said. He then went around the corner and climbed the exterior fire escape to the fifth floor, where he entered the building through a propped-open door.
SEE ALSO: Chicago police Homan Square facility breach raises security questions
How did intruder get inside CPD training facility?
"There's no windows or ventilation on that particular floor, so that door is propped open for ventilation," Supt. Brown explained.
Officers had placed their regular duty weapons on a table in the training room and were using simulation guns. Patrick allegedly took two unloaded guns from the training table and pointed them at officers, Brown said.
Police shoot intruder during active shooter training at CPD facility
In a quick turn of events, the I-Team was told that SWAT officers had to go from training mode to QRF-Quick Reaction Force, and eventually, they shot the attacker.
Patrick, from Waukegan, was previously arrested in Chicago on drug-related offenses as well as car theft, officials said. His motives for the break-in are still unclear.
He has been charged with aggravated assault of a peace officer and three felony burglary counts, police said Tuesday.
"Obviously, someone coming from a stairwell outside startled everyone. Who is this person? Is this person associated with the training?" Brown said. "We do have live actors, sometimes, who come in plainclothes."
WATCH: CPD Supt. David Brown speaks after police shoot intruder at CPD facility
CPD Supt. David Brown speaks after police shoot intruder at CPD facility
"The offender has made some statements that we're going to wait to share, just kind of reconciling his statements with facts," Brown said.
Twenty-six officers were part of the training, including three uniformed officers who are assigned to either City Hall or Mayor Lori Lightfoot's home, Brown said.
Chicago fire officials said the intruder was taken to Stroger Hospital in critical condition. Brown said he is recovering with non-life-threatening injuries.
A police officer suffered a sprained ankle, but remained stable at Mt. Sinai hospital.
CPD facility intruder previously arrested for drug-related offenses, car theft
COPA is investigating. The officers involved will be placed on routine administrative duties for 30 days.
ABC7 Investigative Reporter Chuck Goudie said there could be a full top-to-bottom review looking at how this situation happened at one of the most secure buildings in the city, whether or not it could happen at other buildings and how to prevent it from happening again.
The video in the player above is from a previous report.