Where, upon a trial by jury, a person is convicted of an offense which may be punishable by death, a sentence of death shall not be imposed unless the jury verdict includes a finding of at least one statutory aggravating circumstance and a recommendation that such sentence be imposed. Where a statutory aggravating circumstance is found and a recommendation of death is made, the court shall sentence the defendant to death. Where a sentence of death is not recommended by the jury, the court shall sentence the defendant to imprisonment as provided by law. Unless the jury trying the case makes a finding of at least one statutory aggravating circumstance and recommends the death sentence in its verdict, the court shall not sentence the defendant to death, provided that no such finding of statutory aggravating circumstance shall be necessary in offenses of treason or aircraft hijacking. This Code section shall not affect a sentence when the case is tried without a jury or when the judge accepts a plea of guilty.