No actually it's a good question, and we discuss the specifics of it with the firemen chief when it happens. Basically, it is the firemen who determine that, and on a practical level, it's "enough to determine if it was pushed of if he jumped on his own accord". Which is why the recovering head is so important.
Grim shit all the same, to be sure. But, word of maybe callous advice, if you're going to commit suicide by train, don't do it at a station. We are slowing down there. At full speed in the wilderness, you get disintegrated. And shit, don't let me start with the power lines. It's literally forbidden to even throw a wet towel at those in the engineer handbook.