Human dicer (also known as hsDicer or DICER1) is classified a Ribonuclease III because it contains both helicase and PAZ (Piwi/Argonaute/Zwille) domains [REF].
Current research suggests the PAZ domain is capable of binding the 2 nucleotide 3' overhang of dsRNA while the RNaseIII catalytic domains form a pseudo-dimer around the dsRNA to initiate cleavage of the strands.