When the tanker car incinerates and disappears, it is replaced by substantial flames on the railroad tracks. Yet when the FBI and NASA vehicles arrive seconds later, the flames are gone.
Vincent parks his car in front of a station wagon outside the entrance of his apartment building. When Laura shows up a few minutes later, Vincent's car has moved back to where the station wagon should be, thus allowing Laura to now park outside the entrance.
When David fights with the alien in the tanker, he throws the camera at him, and then leaves without retrieving the camera. Surely that film would be more immediate evidence than what was on the tape. And even if the camera broke he would have taken it with him when he left.
The long telephoto lens David was using outside would be useless inside the train car. Furthermore, assuming he knew how to the night photos, he would be using special film and set the camera to long f-stops to improve his chances at getting good low light level photos. All of these factors would have produced worthless interior photos. He is also never shown changing the focus on the camera, even when he's outside.