Lots of people maintain that crabs with blunt tipped claws (which yours has, the first picture shows that very clearly) are harmless algae eaters. That's a reef myth.
Excuse me, i want to ensure that i understood you properly (English is not my native language)!
You say that crab is dangerous for the tank?
I had one of those in my tank...
What I meant to point out is this...
Mission accomplished. :fun2:
I will post hunt log later. Just for the record - Coca Cola bottle (500ml) with raw shrimp inside works just fine as a trap.