How did the Nuremberg Trials decide whether a guilty defendant was to be sentence to death or life imprisonment?

Question

This page contains a list of Nuremberg defendants, their verdict and sentence. While explanations for lighter sentence (e.g. Dönitz was only sentenced to 10 years) can be found quite easily, many Nazi leaders were sentenced to death or life imprisonment, and it seems quite arbitrary. What criteria did the trials use to decide whether to sentence someone to death or life imprisonment? Was there a precedent for this distinction?

Answer 1

From this summary of the Nuremberg Judgements for major defendants the compilation below is of the finding on Count IV, Crimes against Humanity for each:

Defendant              Count IV - Verdict & Circumstance      Sentence
Martin Bormann         Guilty - no extenuating circumstance   death by hanging
Karl Doenitz           Not Indicted                           10 years imprisonment
Hans Frank             Guilty - no extenuating circumstance   death by hanging
Wilhelm Frick          Guilty - no extenuating circumstance   death by hanging
Hans Fritzsche         Not Guilty on all counts
Walther Funk           Guilty - extenuating circumstance      Imprisonment for life
                          - never took a lead role in the activities in which he participated.   
Hermann Goering        Guilty - no extenuating circumstance   death by hanging
Rudolf Hess            Guilty - extenuating circumstance      Imprisonment for life
                          - the Tribunal did not find enough evidence to find him
                            guilty of these crimes [against the Jewish and Polish people].
Alfred Jodl            Guilty - no extenuating circumstance   death by hanging
Ernst Kaltenbrunner    Guilty - no extenuating circumstance   death by hanging
Wilhelm Keitel         Guilty - no extenuating circumstance   death by hanging
Erich Raeder           Guilty - extenuating circumstance      Imprisonment for life
                          - Limited to violations of Versailles Treaty and 
                          - charges related to unrestricted submarine warfare
Alfred Rosenberg       Guilty - no extenuating circumstance   death by hanging
Fritz Sauckel          Guilty - no extenuating circumstance   death by hanging
Hjalmar Schacht        Not Guilty on all counts
Arthur Inquart         Guilty - no extenuating circumstance   death by hanging
Albert Speer           Guilty - extenuating circumstance      20 years imprisonment
                          - Not a participant in plans for the war
                          - Known to ensure the laborers had food and sufficient
                            work conditions so their work was effective
Julius Streicher       Guilty - no extenuating circumstance   death by hanging
Konstantin von Neurath Guilty - extenuating circumstance      15 years imprisonment
                         - reprimanded personally by Hitler for not being harsh enough
                         - requested release of Czech prisoners in 1939 and 1941
Franz von Papen        Not Guilty on all counts
Joachim von Ribbentrop Guilty - no extenuating circumstance   death by hanging
Baldur von Schirach    Guilty - extenuating circumstance      20 years imprisonment
                         - No evidence that he was aware of plans to wage war

Empirically, it seems that there were two degrees of conviction on Count IV: with and without extenuating circumstance:

• All defendants convicted on Count IV without extenuating circumstance were sentenced to death by hanging
• All defendants convicted on Count IV with extenuating circumstance were sentenced to terms of imprisonment ranging from 10 years to life.

Full transcript of the judgements can be found for most defendants (including Rudolf Hess and Walther Funk).

Update
The Court seems to have found only Count IV without extenuating circumstance to be a Capital Offense; the others apparently regarded as Non-Capital Offenses

Baldur von Schirach may have been lucky - Bulletins describing Jewish extermination were found amongst his office's papers, but no credible evidence was presented that he had actually been made aware of them, or otherwise read them.