PRETORIA, South Africa — Oscar Pistorius came under intense pressure Monday at his murder trial from the chief prosecutor, who dismissed his account of how he killed girlfriend Reeva Steenkamp as a flimsy web of lies and accused the Olympian of staging emotional outbursts to mask difficulty in answering a barrage of probing questions. His voice quavering at times, Pistorius struggled to explain alleged inconsistencies in his testimony and broke down sobbing on two occasions, forcing Judge Thokozile Masipa to temporarily halt proceedings. Prosecutor Gerrie Nel was sometimes quick to acknowledge Pistorius' distress — possibly to allow him time to recover and avoid any defense argument that he is not getting a fair trial — but also said the athlete was frantically trying to shore up a fabricated story.