The plan in both attacks was the same, police said: Two sets of would-be robbers attacked early Tuesday when their victims were in their cars.

And the outcomes of the encounters were almost identical: The intended targets - both off-duty police officers - orchestrated a reversal of fortune. They overpowered their bat- and knife-wielding assailants with firepower from service pistols.

Experts agreed that the circumstances around the two shootings by officers in Deer Park and Elmont are eerily alike and extremely rare.

"This looks like one of those idiosyncratic blips," said David Klinger, a former Los Angeles police officer and senior research scientist at the Police Foundation in Washington. Police-involved shootings are already uncommon, Klinger said, concurring with figures from Nassau and Suffolk police.

Nearly simultaneous shootings - in which off-duty police officers were the intended victims as they sat in cars between 1:30 a.m. and 3 a.m. about 25 miles apart - are still harder to wrap the mind around.

In the first attack, a New York City police officer was on Locustwood Boulevard in Elmont when two men sneaked up and one put a blade to his neck. The officer fired one shot that struck one man in the shoulder.

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In the second, a Nassau detective was vacuuming his car at a self-serve car wash on Lincoln Avenue in Deer Park when he was ambushed by two men with a bat, police said. He fired and struck one man, killing him.

Erik Johnson, 24, of Bay Shore, was pronounced dead at Southside Hospital.

"There's really no way we can say from a social scientific perspective that we can predict these things or explain them," Klinger said.

He said that in New York City, which has more than 37,000 officers, police shot 29 people in 2007, 10 of them fatally. In the same year, the 9,000-officer Los Angeles Police Department shot 33 people, 20 with fatal consequences.

The U.S. Department of Justice's Uniform Crime Report in 2009 said there were 371 "justifiable homicides" by police nationwide in the line of duty in 2008, 368 of which involved firearms. There was an average of 374 fatal shootings over the five years ending in 2008.

Suffolk's 2,537 sworn officers had one case last year in June when an officer fatally fired his gun, and another last August when an officer fatally fired.

In Nassau, there are 2,585 sworn officers. This year, there have been eight cases in which police officers discharged their weapons. In 2008, there were 10.

"It's almost as bizarre as a department not having any shootings at all for 30 years," said Ronald Scott, a firearms and ballistics expert. "It's certainly an unusual set of circumstances."

With Sophia Chang

and Chau Lam