BARDEN CHESS

Alexander Morozevich v Alexey Shirov, Wijk aan Zee 2001. Shirov let a win slip in the diagram where he visualised 1 ... Qb5+ 2 c4 (if 2 Kf2 a4 traps the bishop) Qe5! (threatens both Rxb3 and Qxe3) 3 Qd8+ Bf8 but rejected it because of 4 Bh6. What did Black overlook at the end of this sequence?