Sanhedrin 35 - Capital Cases are not Judged on Fridays
Monetary cases may be concluded on the same day as they have started, however capital cases may be concluded on the same day for acquittal, but only on the following day for conviction. The judges go home at night and consider the matter further, trying to find more reasons for acquittal.
Because of that, capital cases may not be tried on Friday. If the verdict is for conviction, the man has to be executed on Saturday, and that is not possible. Waiting with the execution is not allowed, so as not to prolong the agony. Concluding the judgment on Sunday is also not possible, because the judges may forget the arguments. And even though scribes write down their arguments, they don't write down their thoughts.
Art: Eduard Frankfort- A Theological Debate