In 69 when two commanders of legions refused to renew their vows of allegiance to Galba, Vitellius was proclaimed emperor of both the Germania Inferior and Superior armies. 3 more armies sided with them shortly after.
They marched on to Rome to find that Otho was the present ruler after the death of Galba. It was in fact the senate that recognized his rule and was never acknowledged as emperor by the greater Roman Empire.
Hoping to win the favor of Othos, around 120 people confessed to being a part of Galba’s death. A list of these names was drawn up and after Othos' reign was over, Vitellius had every person on that list executed.
His reign however was to be short lived as he soon found out that eastern armies had proclaimed their commander, Vespasian as emperor. When the armies ruled by Vitellius discovered this he was virtually deserted by his former supporters.