Alena's solution is the correct one.

Shamelin, 1.Bd7 Qh5 2.gh5 Rh8 pushes the mate beyond 4 moves- in fact, I think mate in 6 total is all this line accomplishes.

V-2

1.Bb5 Bb1
2.Bc6 Nf4
3.Nxd5 a5
4.Nf6#

V-3

1.Bb5 Qb1
2.Bd7 Ne7
3.Bf5+ Nxf5
4.Rxe5#

V-4

1.Bb5 Bxb3
2.Bxd3+ Rxd3
3.Re2+ Re3
4.Rxe3#

1. Bd7 (threatening 2. Bf5#)
   a) if 1. …, Ne7/Nh4; 2. Bf5+, N:f5 (forced); 3. R:e5# (MATE IN 3!)
   b) if 1. …, Qh5; 2. g:h5! (still threatening 3. Bf5#), Ne7/Nh4; 3. Bf5+, N:f5 (forced); 4. R:e5#

V-1

1.Bb5 axb5
2.Nxb5 d4
3.c4 h5
4.Nd6#

I will consider another variations tomorrow.