The cross-examination of South African Olympic athlete Oscar Pistorius is due to resume for a fifth day at his trial in Pretoria.
The prosecution has been challenging his version of events on the night he shot dead his girlfriend, Reeva Steenkamp, in February last year.
The double-amputee runner denies murder, insisting that he mistook Ms Steenkamp for an intruder.
He faces 25 years to life in prison if convicted of premeditated murder.
On Monday, prosecutor Gerrie Nel suggested the athlete was staging emotional outbursts to mask his difficulty in answering a barrage of probing questions.
Judge Thokozile Masipa temporarily halted proceedings on two occasions on Monday after Mr Pistorius broke down sobbing.
Shortly before the case adjourned for the day, Mr Nel said: “You’re getting emotional now because you’re getting frustrated because your version [of events] is improbable.”
The prosecutor, known as the “bull terrier” for his fierce style of questioning, then asked: “You’re not using your emotional state as an escape, are you?”
Mr Pistorius said he had not been in a “rational frame of mind” at the time of the shooting.
Earlier, Mr Nel again pressed Mr Pistorius on the moment he shot Ms Steenkamp.
The athlete insisted he had not intended to kill anyone, saying: “I fired out of fear.”
Mr Nel then said Mr Pistorius was changing his story from self-defence to saying he shot by accident.
The prosecutor said this was because the truth was: “You fired at Reeva.”
“It’s not true,” Mr Pistorius replied, bursting into tears and prompting the court to adjourn briefly.
Mr Pistorius said he and Ms Steenkamp had spent a quiet evening together before he woke up on hearing a noise in the bathroom.
Prosecution witnesses have testified to hearing a woman scream, but the defence disputes their testimony.
If Mr Pistorius is acquitted of murder, the court must consider an alternative charge of culpable homicide, for which he could receive about 15 years in prison.
He also faces charges of illegally firing a gun in public and of illegally possessing ammunition, both of which he denies.
There are no juries at trials in South Africa, and his fate will be decided by the judge, assisted by two assessors.
Oscar Pistorius is known as the “Blade Runner” because of the carbon-fibre prosthetics he uses on the track.