The story is supported by material quoted in "The Long Steel Rail," by Norm Cohen, pp. 132ff, especially p. 134, where an article from the Memphis Commercial Appeal, May 1, 1900, is reprinted.
Headline- "Dead under his cab - The Sad end of Engineer Casey Jones - Illinois Central wreck.
"Southbound Passenger Train No. 1 Crashes into the Rear of a Freight- Details of the Accident. .... The Engineer, Casey Jones, was instantly killed and Express Messenger Miller was hurt internally, but not seriously." The news report continues to detail the story much as given in the Brotherhood of Locomotive Engineers history.
"Christened John Luther Jones, the hero of our story was born March 14, 1863...and reared in the town of Cayce, Kentucky.

"Nine years after his death, one song in particular became a national rage: it was a pop song, "Casey Jones," written by two vaudevillians, T. Lawrence Seibert and Eddie Newton, and published in 1909."

Other claims surfaced, both as to the identity of the engineer, but they all came after the 1900 newspaper article quoted above.

Authorship of the song- "The first published reference to a song about Casey Jonesappeared in the March, 1908 issue of Railroad Man's Magazine.....The song is supposed to have been sung by his Negro fireman." This 1908 vesion "is the earliest published text of the ballad." "The ballad text- or something very similar- was attributed to Wallace Saunders by two authorities on Jones history."
In 1910, the mayor of Canton Ohio wrote John Lomax that Saunders was living there, but the Lomax' didn't follow up the story until 1933, by which time Saunders was dead.
Much more is given by Cohen, but these details essentially support the Brotherhood of Locomotive Engineers' story.

The 1908 text is essentially the one we know, and antedates the Seibert-Newton version. Several versions are given by Norm Cohen, which I think have appeared in the DT and Forum.