NYPD has filed no charges against a driver whose boat trailer came unhitched and struck two people riding bikes in Staten Island yesterday, killing one of the victims.

Alexa Cioffi, 21, and another woman were riding northbound on Hylan Boulevard at Redgrave Avenue at around 5:18 p.m. when a northbound driver towing a boat with a truck attempted to pass the cyclists on the left, according to the Staten Island Advance.

As the SUV switched lanes, its trailer became detached and continued to travel north into the right lane, striking the 22-year-old cyclist. The boat was propelled north, hitting Cioffi who became pinned under the vehicle as it stopped.

“They were both hit — thud, thud,” a witness told the Daily News. “One woman was under the boat. The other woman was lying facedown by the light pole.”

Cioffi was pronounced dead at Staten Island University Hospital, the Advance reported. The second victim was hospitalized in critical condition.

If the crash occurred as reported, Cioffi and the other woman were cycling with the right of way when they were hit. But anonymous NYPD sources blamed the victims for their injuries while exculpating the unnamed driver, telling the Post the cyclists were not wearing helmets — which is legal — and that “police did not believe there was any immediate signs [sic] of criminality.”

Meanwhile, the Daily News cited unnamed NYPD sources who indicated that the trailer was not properly attached to the truck.

Sources close to the investigation said the hitch had been modified in some way.

“It came unhitched from the trailer, it wasn’t properly secured,” a police source said.

Streetsblog reader Joe Enoch is a reporter and is currently producing a national story for “Inside Edition” about the hazards of improperly attached trailers. “Unhitched trailers are more common than you think and very often deadly,” Enoch told us via email. Based on a crash scene photo published by the Daily News, Enoch said: “It’s likely the driver did not have either of the two required safety chains. You cross the two chains so that in the unlikely event the trailer comes loose, they safely cradle the hitch. That said, there’s also a good chance that the trailer did not have a proper pin to keep the latch from popping off.”

NYPD had issued no charges or summonses as of this morning. A police spokesperson said the investigation is “ongoing,” which usually means the Collision Investigation Squad hasn’t filed a complete report.