The test in central Pennsylvania showed that the homemade bomb, had it been constructed and detonated properly, would have killed or wounded an untold number of pedestrians and damaged buildings along the block where the car was abandoned by Faisal Shahzad on May 1, the officials said.
"It would have been extremely deadly," Police Commissioner Raymond Kelly said Tuesday when asked about the test after an event at a Washington think tank.
Kelly didn't go into specifics about the FBI test. But two other officials told The Associated Press that it was conducted late last month in a remote area 30 miles outside of State College, Pa., and that a video of it was played for a gathering of authorities earlier this week.
The officials spoke to the AP on condition of anonymity because they were not authorized to speak publicly about the test. The FBI's New York office declined to comment.
The test was first reported Tuesday in the New York Post, which quoted an unnamed source saying that the results suggested the bomb could have been more deadly than the 1995 Oklahoma City car bombing that killed 168 people. One of the officials who spoke to the AP said that was an exaggeration, because the Oklahoma City bomb - also made of fertilizer - was roughly 10 times larger than the one left in Times Square.
Calling himself a "Muslim soldier," Shahzad pleaded guilty June 21. During his plea hearing, the 30-year-old traced his plot to a 2009 trip to Pakistan, where he said he received explosives training and funding from the Pakistani Taliban for his one-man scheme. He returned to the United States and loaded a 1993 Nissan Pathfinder with a fertilizer-fueled bomb packed in a gun cabinet, a set of propane tanks and gas canisters rigged with fireworks that he hoped would cause a chain-reaction explosion.
After parking the vehicle on a street near Broadway theaters and hotels, Shahzad said he lit a fuse that he expected would detonate the bomb within five minutes as he walked away. Instead, authorities say the bomb malfunctioned, emitting smoke that attracted the attention of a street vendor, who notified police.
Federal agents arrested Shahzad two days later as he attempted to flee the country on a Dubai-bound jetliner.
New York Police Department bomb experts later determined Shahzad had used a type of fertilizer that wasn't volatile enough to explode like the ammonium nitrate grade fertilizer used in previous terrorist bombings. Kelly said Tuesday that investigators believe Shahzad purposely "dumbed down" the bomb - using the less potent fertilizer and M88 firecrackers - to avoid detection.
For the test, the officials said the investigators also used a Pathfinder but rigged it with the higher grade fertilizer and more sophisticated components. Four other vehicles were positioned around the car bomb in positions replicating cars in an adjacent traffic lane and parking spots in Times Square.
The explosion obliterated the SUV, cutting it in half, the officials said. It also turned the car next to the SUV into a flaming wreck, and sent it flying for a distance that in Times Square would have vaulted it over a car parked across the street and into the New York Marriott Marquis.
Two other cars were left in one fiery, tangled wreck in the middle of the mock street, the officials said.