If payments were made of salary, there should be tax records reflecting the payment of that salary. Presumably this was not payment to an independent contractor, although if it were there should still be 1099's, because independent contractors don't get overtime pay.
If these people are alive, and yet proper payroll and tax records were not maintained, it should be possible to produce them and have them testify as to the money they received and what it was for. Also, there should be endless cancelled checks showing who received the money and where it was deposited.
So the defense needs to follow the paper trail, and assemble its witnesses.

