Firefighters responded to the building on North Avenue shortly after 12 a.m. Thursday after reports of smoke coming out of one of the apartments.
First responders found what appeared to be damage from an explosion that went off in the hallway outside one of the apartments located on the third floor.
20 families were evacuated from the building while it is being searched for evidence and possible secondary devices, although none were found.
In all, 134 people who live in the general area were displaced. No injuries were reported.
Police say Nelson Diaz, of Bridgeport, was taken into custody shortly after the explosion and has since been charged with disorderly conduct.
Diaz was seen roaming the hallways of the apartment building on North Avenue shortly before the blast, then "walking briskly to his car seconds after the explosion," police said.
FBI bomb technicians are working to determine the exact type of device. Officials said the initial call was for "possible fireworks."
Residents will be able to return "soon," said Bridgeport Mayor Joe Ganim, but "there is some serious damage to the front entrance way" of the building.
Nearby Geraldine Johnson Elementary School was closed Thursday, because it was being used by evacuated residents.
North Avenue was closed between Oak Street and James Street as the investigation continued.
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