There is evidence that it was premeditated. From the article:
> They [the jury] heard how he had joked about “a murder plan” involving tying up a woman on his submarine and slitting their throat with a knife in a set of messages sent to a friend, which he had subsequently tried to delete.
> They [the jury] heard how he had joked about “a murder plan” involving tying up a woman on his submarine and slitting their throat with a knife in a set of messages sent to a friend, which he had subsequently tried to delete.