Prosecutors are exploring whether Testwell falsified some test results, double- and triple-billed for some tests and charged clients for tests the firm never conducted, the official told the AP.
The $1.3 billion new Yankee Stadium - being built across the street from the team's former home in the Bronx - is a focus of the probe, as is the Freedom Tower, the 102-story skyscraper being built to replace the destroyed trade center at ground zero, the official said. Up to a dozen other projects also may be involved, the official said.
A Yankees spokesman and the trade center site's owner each said Friday that independent tests had been conducted on the concrete Testwell tested, and the projects were structurally sound.
E-mails and telephone calls to the company's Ossining office and an attorney weren't immediately returned Friday.
The city - which has cracked down aggressively on construction companies amid a record building boom and several deadly accidents - couldn't immediately say how many construction projects Testwell has worked on. The Department of Buildings said it would "take action based on the findings of law enforcement."
Testwell conducted tests for concrete poured at the Freedom Tower between April and September 2006, said Steve Coleman, spokesman for the site's owner, the Port Authority of New York and New Jersey. The agency - which has its own concrete-testing staff - took over Testwell's work in September 2006, when it took control over building the skyscraper from private developer Larry Silverstein, Coleman said Friday.
The agency found "irregularities" in previous tests submitted by Testwell and referred the findings to its inspector general's office, who turned it over to Manhattan prosecutors earlier this year, Coleman said.
Coleman wasn't sure how much Testwell-tested concrete had been poured into the tower's footings, but he said two engineers conducted separate tests, and both "deemed that the Freedom Tower is safe."
The tower's builders removed a small amount of concrete in March and April from the Freedom Tower's foundation after tests showed the concrete was below strength; Coleman said Testwell had never handled that concrete.
A Yankees construction monitor first discovered some problems with Testwell's work on the stadium project in February, and the team has cooperated with a law enforcement investigation for several months, Yankees spokesman Howard Rubenstein said in a statement.
Independent testing also found that "the entire concrete process was structurally sound," Rubenstein said.
The team is building the stadium - financed mostly with tax-exempt public bonds - to open in 2009. The 1,776-foot Freedom Tower is scheduled to open by 2012.
