It was unclear as to why the Baron trusted Marko but now knowing how the baron knew the fact that marko lost his father and it was the baron who killed his father.
But how did he know? That day the baron was send to a city where revolt was being reported. Under the orders of previous Emperor who were the friend of the Baron decided to go towards the city to deal with the issue.
To ensure the Emperor's will is absolutely especially when he was seen sickly and weak. The baron decided to show no the mercy.
The baron simply wanted to use fear to prevent more revolts so that his friend can have a smooth ruling period than a rough one. So he decided to do things the hard way which was to murder enough protestors so others will run away and won't return.
The day baron arrived to the city, he was directly came to the centre to meet the city administrator who told him the situation was getting worse.
