I killed all the smugglers in Gandrung Caverns, returned to Captain Carius, but he still asked me to find the smugglers? is there anyway to override with a code to complete this mission, cheers.

While at Gandrung Caverns try typing in the console command "SetJournalIndex BM_Smugglers 97"

This will give you a journal update that you have defeated all the smugglers. Once you get back to Frostmoth, you won't have to the opportunity to talk to Carius and should get the final journal entry of the quest.

thanks now on to Thirsk! I think I bugged it by leaving the quest because I was low level and come back after the telvanni quest, cheers...