Jim Fisher's two books on the kidnapping are definitive. He went right back to the original evidence which is kept in a State Police archive/museum in New Jersey. Don't bother reading anything else about the case. Fisher's investigation was exhaustive, and he has a police investigative background. The baby was killed shortly after the kidnapping, and Hauptmann was clearly guilty.
I also have the book by a highly respected handwriting examiner who testified at the trial that was published after the trial with many photostats of the kidnap letters and Hauptmann's known handwriting. Believe me, they match.
Over the years, there have been many fake Lindbergh babies and many stupid "theories" about the case. This is just one more example.
1. Hauptmann spent some of the ransom money.
2. Lumber from Hauptmann’s attic was used to make the ladder.
It seems to me the outstanding issues were:
A. Were their some accomplices who were not caught who spent some of the money.
B. The ladder was poorly made and Hauptmann was a carpenter. Hauptmann’s defense claimed a German visitor who stayed with Hauptmann and went back to Germany and died shortly had the access to the lumber and spent some of the money and maybe was the real kidnapper?
It seems to me that points A and B might be related.