After hearing all of the evidence and arguments in the sentencing proceeding, the judge or judges shall fix the sentence at either death or life imprisonment, but such determination shall be based upon the following considerations:
(1) Whether sufficient aggravating circumstances exist to justify imposition of a sentence of death;
(2) Whether sufficient mitigating circumstances exist which approach or exceed the weight given to the aggravating circumstances; or
(3) Whether the sentence of death is excessive or disproportionate to the penalty imposed in similar cases, considering both the crime and the defendant. In each case in which the court imposes the death sentence, the determination of the court shall be in writing and shall be supported by written findings of fact based upon the records of the trial and the sentencing proceeding, and referring to the aggravating and mitigating circumstances involved in its determination. If an order is entered sentencing the defendant to death, a date for execution shall not be fixed until after the conclusion of the appeal provided for by section 29-2525.