What's the misunderstanding that brings the play to its tragic end?

Maria sends Anita to Doc's to tell Tony that she has been detained, but at the store, members of the Jets harass Anita. In her anger and dismay at having nearly been molested, Anita lies and tells Doc and the gang that Chino has killed Maria in a fit of rage. Doc sends the ruffians away and gives Tony Anita’s devastating false news. A distraught Tony then mindlessly runs out into the street, taunting Chino to kill him as well.