Are you trying to say that if a mechallel Shabbos convict escaped after conviction but before execution, if he is caught 25 years later he can be executed?
I would have to learn the sugya again to be certain, but I believe that to be the case.
Of course, the rules of testimony in the new case are the same as in the old case. Two witnesses who witnessed the conviction would have to testify to the conviction (not to the actual chillul Shabbos).
And does it matter if he was convicted and sentenced by beis din (is there even a “sentencing phase”?) or if he escaped after conviction but before sentencing?
There is no sentencing phase. The penalty is already set by the Torah.
Indeed, upon conviction of a capital crime in beis din what is the procedure? Is he immediately taken to the place of execution, or are there other formalities first?
The convicted is taken for execution immediately. However, he is allowed to try to put forth new arguments for his acquittal. Each time he is returned to the Bais Din. However, after a few times, he is only returned if there is substance to his arguments.
The Wolf