Cicero was a great lawyer but in the 63 b.C. during his consulate, after the Senatus consultum ultimum, he made to execute the coniurati friends of Lucius Segius Catilina not respecting the roman criminal law.
No roman citizen in fact could be executed without the ratifies of the roman people to the senatus sentence of dead. Cicero not asked to the roman people its judgment.
Marcus Antonius will never pardon this legal abuse to Cicero and will write in the list of prescrizione first the name of Cicero.