"The people who did this obviously knew what they were doing," McGinnis said.
A crane, an excavator, a bulldozer, a large compressor, and a pile hammer were damaged, said Bob Behn, a project manager for Walsh Construction.
The compressor had been pushed into the Delaware River, Behn said.
"Even the Porta-Potties, they ran them over and crushed them," McGinnis said.
Because the company is using local union workers, labor-related vandalism has been ruled out, McGinnis said.
Detectives were told the bidding process for the project was "extremely competitive," so that angle is being investigated, McGinnis said.
In June, the Pennsylvania Department of Transportation announced it had awarded a $212.3 million contract to Walsh for rebuilding a portion of I-95 in Northeast Philadelphia.
Officials said it was the largest contract ever awarded by the agency.
The site was surrounded by a fence and locked gate, which was not breached, McGinnis said. There is a small dock on the Delaware, so detectives believe the saboteurs may have arrived by boat.
Work has stopped at the site until a security system is installed, Behn said.
Contact Robert Moran at 215-854-5983 or firstname.lastname@example.org, or follow @RobertMoran215 on Twitter.