“ If the Sixth Amendment permits a judge to impose a sentence of death when the jury recommends life imprisonment, however, it follows that it does not forbid the judge to make the written findings that authorize imposition of a death sentence when the jury unanimously recommends a death sentence. ”

“ In the order imposing the death sentence, the trial judge found four aggravating circumstances: petitioner had previous convictions for violent felonies, he was under a sentence of imprisonment at the time of the murder, the killing was committed for pecuniary gain, and the killing was especially heinous, atrocious, and cruel. ”