NYPD investigators have reportedly been unable to determine which officer's gun fired the fatal shot that took the life of a detective from Long Island.

According to Newsday, investigators have been unable to make the determination in the friendly fire shooting death of Detective Brian Simonsen, of Calverton, even though the round that killed him was recovered.

News 12 is told that the round that struck Simonsen's partner, Matthew Gorman, of Seaford, has not been recovered.

As News 12 has reported, the two were struck by friendly fire while responding to a robbery in the Richmond Hill section of Queens earlier this month.