In what sense, before he reaches Sirael? And does it take one turn to attempt to pick a lock?
And if he doesn't notice during the first kill, I thought I'd try cutting down the locks one by one before picking them.
Then they will have a chance to notice you when you are killing them.
Added after 9 minutes
Let me clarify one more thing: if you kill one, the other has a chance to notice something is wrong, and you won't be able to sneak up on him or use the assassin skill.
Небо – угроз не слышит
Небо – ведёт особый счёт
Небо – тебя найдёт