 NTSB head Robert Sumwalt told reporters two days after the crash that it was too early to say whether the limo had been speeding at the time; the agency was focusing on human and mechanical factors as causes.It was, however, a "high-energy impact" that had severely damaged the front and left portions of the vehicle, and, Sumwalt intimated, driven the engine into the passenger compartment.There were no skid marks on the pavement, suggesting the driver had not applied the brakes, or that they had not been functioning well, before reaching the stop sign.