The National Transportation Safety Board, which has yet to determine the cause of the crash, concluded talking with the engineer on Tuesday.
Investigators continued interviewing the train's other crew members.
Investigators have said Rockefeller had enough time off for a full night's rest before the crash, but they were looking at his activities in the previous days.
Rockefeller's schedule, which had recently switched from the afternoon shift to the day shift, could be a cause for concern about fatigue, said Patrick Sherry, executive director of the National Center for Intermodal Transportation at the University of Denver, which studies national transportation issues.
Federal investigators would not comment on Rockefeller's level of alertness. The NTSB had found no problems with the brakes or rail signals.
Alcohol tests on crew members were negative, and investigators are awaiting the results of drug tests.
Rockefeller, 46, has worked for the railroad for 15 years and has been an engineer for 10.
