Then, they partially detonated it.
The 2004 experiment, revealed by city officials Tuesday, was part of a New York Police Department program to monitor suspicious sales of ammonium nitrate and other common chemicals sold by suppliers in the New York City area.
Testifying in Washington, D.C., before the Senate committee on homeland security, the NYPD's top counterterrorism official, Richard Falkenrath, said the $7,000 operation "proved the ease with which the fertilizer can be legally obtained and used as part of an explosive device."
Authorities did find out about the purchase before the team partially detonated the bomb, but it was unclear whether a real-life plot would have been foiled.
Falkenrath, a former national security aide for the Bush administration, criticized Congress and the White House for failing to seek strict regulations on the sale of ammonium nitrate fertilizer, a key ingredient in the bomb used in the attack on a federal building in Oklahoma City in 1995.
"It has become commonplace to ask why, five years after Sept. 11, certain security enhancements have not been implemented," he said, according to a copy of his prepared remarks provided by the police department. "In this case, the question is, why has nothing been done about ammonium nitrate more than 10 years after the Oklahoma City bombing?"
Police officials in New York later detailed how investigators with no experience in explosives had posed as apple growers in two purchases of more than 1,000 pounds of fertilizer from agricultural supply outlets in Schaghticoke, N.Y., and Yardley, Pa. (The New York seller later became suspicious and reported the sale to federal authorities, who learned about the undercover operation while trying to do a background check on the phony purchasers.)
The officers rented space at a self-storage facility in the Bronx to stash the fertilizer and other chemicals, including fuel oil. They later put the fertilizer in a van similar to one used in the 1993 bombing of the World Trade Center.
They drove to an outdoor police shooting range in the Bronx, where they cooked up explosives using recipes from the Internet and widely available books. But out of fear that the bomb was big enough to destroy the facility and frighten residents, only a portion of the explosives was detonated using peroxide-based blasting caps.
Police Commissioner Raymond Kelly said the operation "demonstrated that safeguards are needed to make it harder to acquire bomb-building material and easier to regulate and track their sales."