Another NYPD officer was wounded during the incident and was rushed to the hospital along with Simonsen where he was pronounced dead.
Arwindern Singh, who lives across the street from the store, said he heard about 20 shots go off and thought they were firecrackers.
The NYPD is dealing with the loss of one of their own after two officers were shot, one fatally, while responding to an attempted robbery in Queens Tuesday night.
"Tonight highlights the incredibly fearless actions NYPD members perform each day in the name of fighting crime and keeping people safe in every neighborhood".
Responding to reports of a robbery, Sgt. Matthew Gorman and two uniformed cops entered the store just after 6 p.m.to find it seemingly empty - until Ransom ran out of a back room pointing the phony firearm at them and squeezing the trigger, officials said at a Wednesday press briefing.
"This appears to be an absolute tragic case of friendly fire", said O'Neill, who added that the assessment is subject to change pending an investigation.
The suspect, who was also shot, is now at a nearby hospital and under arrest.
The suspect, identified as Christopher Ransom, was also shot during the encounter and hospitalized, officials said.
Mayor Bill de Blasio and several other city officials are at Jamaica Hospital Trauma Center.
"Make no mistake about it, friendly fire aside, it's because of the actions of the suspect that Det".
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The suspect is dead, it's reported by NY1.
Ransom was taken to the hospital where he will later be released into police custody.
"We lost a very good man, Detective Brian Simonsen", said Mayor Bill de Blasio.
Another officer, a sergeant who was shot in the leg, is listed in stable condition. Simonsen earlier Tuesday. An elected delegate with the 102nd detective squad, Det.
Down the block from the 102, the Daily News front-page photo of Simonsen has been taped to the window of the grocery store where the detective was a regular customer. "All-time, all the time, he come in my store, all times", one worker said.
Simonsen should've been off Tuesday for a union meeting, but he opted to go to work so he could continue tracking a string of recent robberies, Detectives' Endowment Association president Michael Palladino said.
"He was the kind of fellow who led by example", Palladino said.
"He always asking us, 'How's things going?' He was always there for everybody when people need him", another worker said.
His death marks the first New York City officer killed in the line of duty since July 2017.
Officers responded and fired multiple rounds, during which Simonsen was hit, the commissioner informed.