life without parole; first-degree murder; robbery with a dangerous weapon; assault with a deadly weapon with the intent to kill inflicting serious injury; involuntary confession; extrajudicial confession; induced hope or fear; totality of the circumstances; question of law; threats; promises; de novo; incriminating statements; Fifth Amendment; voluntariness of a confession; leniency; lesser sentence; constitutional error; harmless beyond a reasonable doubt; accomplice; prejudicial error review