Former US attorney Joseph diGenova said criminal charges were possible if either Firestone or Ford misled the government.
Jac Nasser, Ford chief executive, told a Congressional hearing: “Ford did not know there was a defect with the recalled tyres until we virtually prised the claims data from Firestone's hands and analysed it.”
Ford has shut production at three Explorer plants at a cost of around £125m to free tyres for the recall. It has agreed, in principle, to help Firestone pay some of the costs.
US lawyers are investigating whether Ford knew about the tyre problems earlier and whether it deliberately advised customer to under-inflate tyres to disguise handling problems.