Perez's aunt said her nephew held various jobs and was now working, though his aunt and her family did not know where. One of the victims died at the scene. The building serves as the corporate headquarters of Fifth Third Bank.
Details of the shooting were not immediately available, but the dispatcher said the situation is no longer active, and a suspect is in custody.
During the press conference, the Cincinnati Police Department showed the body camera footage of officers firing shots into the building.
Newcomer was doing work on the third floor of the building and "just happened to be at the wrong place at the wrong time", Cotter said.
"A very horrific situation", Isaac said at the scene.
"Then we knew what was going on", Hanson said.
Leonard Cain, one onlooker, told the Cincinnati Enquirer that he was about to enter the bank when someone warned him about the shooting.
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A Cincinnati city council official said there had been "fatalities" with police warning of an "active shooter". Cook said she and two other employees hid in the bathroom for the duration of the shooting. "Apparently there were shots below, and then he moved up to the lobby".
Hamilton County Prosecutor Joe Deters said the rapid police response probably prevented many more casualties. At least four people have been taken to hospital.
A witness said he heard up to 15 shots. "After that I started running", he told the Enquirer.
Perez is a US citizen born in San Juan, Puerto Rico, family members said Thursday.
"This is clearly an act of grotesque violence to innocent people and it should frighten all of us", said Cincinnati Mayor John Cranley.
Four of the five victims - three of whom died - have been identified by either authorities or family.
Police didn't reveal a motive for the shooting.
A visitor from Germany sat at a table on Fountain Square, enjoying a sunny morning when he heard some teens shouting about a shooting.
Fountain Square is host to concerts, food trucks and many retail shops.
Witness Cheryl Eagleson said she was across the street from the bank when she heard "loud pops" from a gun, prompting people to drop to the ground. Our thoughts and prayers are with everyone caught up in this awful event.