The criminal laws of the US date back to the 19th century, when everyone pretty much stayed put and didn't move around much. This gives a procedural advantage to the drunk who punches a conductor on a moving train. Although assault on an Amtrak conductor is a federal offense, the US Attorney is probably not going to be interested. Therefore you have to get the information in front of the D.A. of Podunk County, or wherever the miscreant was at the moment he threw the punch.

I assume that Amtrak has its conductors write up a report. This should be forwarded to the DA, along with the report of the police officers who took Mr. Drunko off the train, recounting their experience with him.

The next challenge is getting the DA to file a serious charge. Our is an alcoholic country, and so DAs see lots and lots of drunken brawls. It's necessary to convince the DA that an assault on a conductor is not an ordinary drunken brawl. One thing is that the conductor, who has some skin in the game, should bird-dog the DA, including if necessary making a trip on his day off to Podunkville to meet with the DA (Of course, in a perfect world, Amtrak would pay his wages for this, but anyway).

The next challenge is getting the jury to convict. The pitch here, I think, is not that the victim is "Amtrak." The jury doesn't know Amtrak from a hill of beans. The pitch is, "I was trying to do my job and this drunken bozo prevented me." Jurors understand work.