All chords in this case file are played in root position — root, third and fifth stacked in order, no inversions. A new suspect has joined the line-up: vi, the tonic's minor double.
Reference the suspects before the case opens. Tap each one as many times as you like.
The vi chord joins I, IV and V, all in root position. Students start to hear the minor sound of vi against the three major chords.
Pairs well with pop songs, since so many of them use I, V, vi and IV. Play one first and see if students can pick where the minor chord is.