The crime was committed within the Mandate against the Mandate, interfering with the investigation is at odds with Imperial sovereignty; when avowed enemies of the Empire seek to degrade its sovereignty, it is the duty of the Imperial Navy to obstruct them. When the Empire’s foes overcome its border militarily, that is by definition an incursion by hostile forces.
Your Republic would spend every single life in its fleet before accepting Imperial jurisdiction in their borders, that is roughly how enamoured we would be to accept Republic jurisdiction within the Empire.
No such demands have been made of the Republic, they disavow too promptly for anyone to be afforded the opportunity to demand, and the Elder Fleet taught us how much faith to place in their justice.
None was meted out for that, I expect no more for this.