NYPD investigates whether Frank James tested grenades at Floyd Bennett Field

Police are reportedly investigating the possibility that accused subway terrorist Frank James may have conducted a test run of his attack by throwing smoke grenades at Floyd Bennett Field in Brooklyn.

After James was arrested on Wednesday, the NYPD received a tip that a van — possibly a U-Haul — had been sighted in the area of ​​the airfield the day before and that someone may be detonating smoke grenades, WNBC reported, citing law enforcement sources.

However, investigators told the news outlet that it was too early to determine if the white vehicle and explosives were linked to the suspect in the subway attack.

James is suspected of opening fire on a Brooklyn subway car, shooting and injuring ten people and injuring 19 others, during Tuesday’s morning stampede.

James was arrested by the NYPD in Manhattan’s East Village on Wednesday after calling the NYPD Crime Stoppers hotline and telling police to come and pick him up at a local McDonald’s restaurant.

Federal prosecutors charged him with terrorist attacks and other mass transit violence, which, if convicted, could lead to life imprisonment.

In the early aftermath of the attack, officers had trouble locating James because the surveillance cameras at the 36th Street station where the incident occurred were not working.

They later found James had mixed in with the commuters and took an R train to the next stop on 25th Street, where the cameras also didn’t work.

The suspected gunman, who previously stayed in an Airbnb in Philadelphia and also has ties to Wisconsin, rode into the Big Apple in a U-Haul truck early Tuesday morning around 4 a.m

Surveillance footage showed him walking over the Verrazano Narrows Bridge and driving into Brooklyn, where a U-Haul van he rented on April 6 was later found abandoned in Gravesend, court records show.

James is scheduled to appear in court on Thursday.