There is some history that’s not explained in the book, and that I’m not completely privy to all of it
However, it is my understanding that Asmeth and his crew have had many a run in with the Oorstemothians for their smuggling and a Warrant of High Justice had been issued for him and his crew. Under such circumstances, once they were able to positively identify and document he and his ship, they were authorized to execute the Warrant.
Which they summarily tried to do.
I should note that one of the more recent incidents involving Asmeth and his crew was in smuggling a group of tomb raiding rogues out of Oorstemoth with a valuable artifact that, at first, the authorities thought was given to Exador, but was in fact, given to Lenamare. There was quite a bit of legal wrangling on that as Exador had to extricate himself from the false evidence that Lenamare had planted on the rogues.
Now, the rogues are still alive, because they have to testify against Lenamare, but they require no testimony on the part of Asmeth’s crew (or didn’t until now) because the rogues had all positively fingered Asmeth and combined with Asmeth’s long history of illegal activities, a court issued the Warrant of High Justice.