O'Neill said as the suspect advanced toward them, the officers discharged their weapons and retreated out of the store.
Sgt. Matthew Gorman was shot in the leg, O'Neill said. He is in stable condition, according to the commissioner.
It was unclear how either officer was injured, or what happened to the suspect.
Gunfire erupted after police responded to reports of an armed robbery at the T-Mobile in Richmond Hill around 6.15pm Tuesday.
Sen. Chuck Schumer said, "We are forever indebted to the courageous NYPD detective who was killed in Queens tonight and the sergeant who was wounded".
"The moment the NYPD Detective was murdered in Queens on Tuesday night at a robbery in a T Mobile store".
"He was definitely shot, he was limping then after that more cars came and there was more shooting", Jason Parodi said.
Det. Brian Simonsen was shot and killed by possible friendly fire during the armed robbery at a T-Mobile store in Queens.
The 27-year-old suspect - a career criminal - pointed what appeared to be a gun at them.
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The department said it will conduct an on-site visit in a few days and is working with the facility on infection control methods. According to another study, one potential cause of these mumps outbreaks is 'waning-immunization.' .
When he went outside, he said "all of a sudden there were cops all over".
A witness told the NYDN that before police arrived, one of the robbers, dressed in black, could be seen escorting two employees to the back of a T-Mobile store at gunpoint. Police recovered an imitation firearm at the scene. Some walked together in a line, searching for evidence.
Mike Palladino, the president of the Detective Endowment Association, also praised Simonsen for his bravery and noted that he had given his life on a day that he could have been at home with his family.
At Jamaica Hospital, officers guarded the emergency room entrance as O'Neill and Mayor Bill de Blasio met with Gorman and offered their condolences to Simonsen's wife and mother.
Brian Simonsen was the first NY police officer to die in the line of duty since July 2017.
"It was heartbreaking to see", NYC mayor Bill de Blasio said.
Officer Miosotis Familia, 48, was writing in her notebook when ex-convict Alexander Bonds strode up and shot her through a window. The officer had planned to retire soon. In December, an officer on Staten Island was hit by friendly fire as officers responded to a domestic dispute call.
Balsamo reported from Washington.
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