Indeed, all you can do until the potential next assassination attempt is wait.
A week goes by and nothing out of the ordinary happens. Senator Farl makes some announcements to Triskatan as a whole updating them on his status and apologizing for not being out in the public, but he hopes they understand that his life is at risk and his Tower is the safest location he can be in.
Drufter says he has put the paperwork in to transfer Emso to the Tower, but it is easier to put people in his jail than it is to get them out, especially as the Tower is not a designated prison facility.
You hear nothing more from Altar.
Nartholen and Walder do awake in this time. They have little to tell, but what you learn is helpful.
When they walked into the basement level of Farl's apartment, they saw someone hunched over the device that you confiscated, working it diligently. They could not see much of him, but they do describe him wearing some sort of face mask... which matches the description of the assassin you chased!
There are more than one.