Did Alexei mention the new arrivals shelf in dialogue? It won't be active if he hasn't.
A couple of tips from MaG in an older thread with the same issue:
Talk to him after Nancy eavesdrops about losing the evidence locker key and asking the others to follow the detective. Then after following him - end up at the antiques store.
Did you follow the trail or stopovers of the detective starting at Pancake City?
"Bleat, Watson -- unmitigated bleat!" ~ Sherlock Holmes