Need help on the Tingalf quest too...

I got the 2 manuscripts, told Robin about it and he arrested Tingalf.

I got the exp gain from marcus the merchant (the one who asked me to replace the wheel), as well from robin (for the arrest), but I can't get trevor the merchant guild master to acknowledge the arrest!

Even tho I have the quest entry from trevor, I don't have any dialogue option to tell him that tingalf has been arrested.

Did I miss a step somewhere??