This is a good question.
After the assassination, Brutus tells the senator and the people not to worry that freedom has been reestablished. The potential tyranny of Caesar is no more. To use the language of Brutus, "the serpent in the egg has been killed."
When Brutus proclaimed freedom, he was incredibly sincere. He even had the conspirators drench their hands in the blood of Caesar to show that they committed this act. In some ways it had a religious tone. From this perspective, Caesar can be seen a sacrifice and the conspirators as priests.
From a historical point of view, Brutus calms the people, because often times the death of a power man could lead to death of political foes.
In the end, Brutus misinterpreted the people's desires.