(CNN) -- Oscar Pistorius didn't consciously pull the trigger the night he shot and killed his girlfriend, the sprinter testified at his murder trial Tuesday.
The Olympic and Paralympic athlete said he was "overcome with a sense of terror and vulnerability" before he shot through a closed bathroom door last year, fearing an intruder was inside.
Defense attorney Barry Roux asked his client what he meant when he referred to the shooting as an "accident."
"I mean the situation, and the situation as a whole, it wasn't meant to be," Pistorius said.
The double amputee said he was terrified when he heard the sound of the toilet door opening.
"I didn't think about pulling the trigger. As soon as I heard the noise, before I could think, I pulled the trigger," he said.
The testimony came after the prosecution ended five days of grueling cross-examination, which has seen the athlete break down on several occasions.
Valentine's Day card
Pistorius cried and his voice trembled as prosecutor Gerrie Nel challenged his account of what happened the night he shot and killed his girlfriend, Reeva Steenkamp.
Nel asked who should be blamed for shooting his girlfriend on Valentine's Day 2013.
"I'm not sure, my lady," Pistorius said, directing his answer to the judge. He repeatedly said he feared for his life and thought there was an intruder in his bathroom.
A day earlier, Pistorius testified, "I blame myself for taking Reeva's life."
He became emotional as he described finding his girlfriend slumped over by a toilet after shooting her through a closed bathroom door.
"I was saying, 'Baby hold on. Jesus, please help me,' " he said Tuesday.
Nel has accused Pistorius of "tailoring" his version of events to suit his story. He questioned Pistorius on details after the shooting that the athlete said he doesn't remember, such as what exactly he did with the gun immediately afterward and who connected his cell phone to a charger in the kitchen.
The prosecution contends that Pistorius shot Steenkamp intentionally after a heated argument, which Pistorius has repeatedly denied.
The defense ended its re-examination of Pistorius by giving the court a piece of evidence: the Valentine's Day card that Steenkamp wrote to Pistorius.
Pistorius read the card aloud.
"Roses are red, violets are blue," he read, his voice cracking. "I think today is a good day to tell you that I love you."
The defense called expert Roger Dixon as its next witness to take the stand at the Pretoria court.
The forensic geologist was brought into the case to analyze the lighting conditions in Pistorius' home, specifically the main bedroom and connected bathroom.
The defense team will call 14 to 17 witnesses, Roux said when he opened his case. The trial is scheduled to continue until the middle of May.
Judge Thokozile Masipa will decide the verdict in collaboration with two experts called assessors. South Africa does not have jury trials.
The trial has gripped South Africa and millions of sports fans around the world who saw Pistorius as a symbol of triumph over physical adversity.
His disabled lower legs were amputated when he was a baby, but he went on to achieve global fame as the "Blade Runner," winning numerous Paralympic gold medals on the steel blades fitted to his prostheses.
Only those in the courtroom saw Pistorius on the stand because he chose not to testify on camera. His testimony could be heard in an audio feed.
CNN's Marie-Louise Gumuchian contributed to this report.