A court filing suggests James Liang's cooperation could help with prosecutions of other workers.

A judge has stalled a sentencing hearing for James Liang, the first former Volkswagen employee to face charges in the diesel emissions scandal, as he continues to cooperate with investigators and prosecutors.US District Judge Sean Cox ordered the hearing pushed from February 1 to May 3 "to allow more time for defendant's cooperation in the investigation," according to a court filing spotted by Reuters.

The documents suggest Liang's participation could lead to the "potential prosecution of others," presumably current and former VW employees.

Liang signed a plea agreement in September, admitting that he and his team designed the illegal 'defeat' software after deciding that the new diesel engine could not meet customer expectations "as well as new, stricter US emissions standards."

Engineers with direct involvement in the cheat may be the low-hanging fruit for US criminal prosecutors, but investigators are almost certainly attempting to build cases against higher-level managers and potentially top executives as the investigations stretch into 2017.