Johann asked:
Could he have been at a place where 24 were assigned to jury duty?
I doubt that there is anyplace in the U.S. where this would be the norm. But, anything is possible.
Here is what might happen: In enpanneling a jury the judge selects a stated number who are immediately part of the jury. In addition, the judge selects a number of additional people who become alternate members of the jury. They attend the trial, listen to the arguements, view the evidence and are subject to the same rules as the members of the jury. In the event that a member of the jury becomes unable to fulfill their duties, or is discharged for any reason, the judge selects one of the alternate members to fill the vacant place.
I can immagine that in the case of a complicated trial that was expected to last for months prior to going to the jury for a decision that the judge might select 12, or even more, alternate jurors. But, this would not be typical.