JOHANNESBURG, South Africa - An expert witness called by the defense team of South African Olympian Oscar Pistorius testified about bullet wounds, blood spatter, bruises, ballistics, sound, light, fibers and a toilet door - but acknowledged Wednesday that he wasn't a pathologist or ballistics expert and had no training in analyzing blood spatters.

Forensic geologist Roger Dixon initially was called in by the defense team to look at gunpowder residue. But under cross-examination he said he ended up looking at a wide range of issues in which he had little or no expertise.

Prosecutor Gerrie Nel accused him of irresponsibility for doing so.

"You gave evidence, you were strong about it," said Nel, referring to pathology evidence Dixon offered. "Do you see how irresponsible it is to give evidence on areas you are not expert?"

Police ballistics expert Chris Mangena, pathologist Gert Saayman and another pathologist called by the defense, Jan Botha, all found that Pistorius' girlfriend, Reeva Steenkamp, was hit by three bullets behind a door. Dixon determined she was hit four times.

Pistorius, the first athlete to compete in the Olympic Games on prosthetic limbs, shot and killed Steenkamp on Valentine's Day last year. Pistorius has pleaded not guilty to murder, contending he didn't intend to kill anyone and didn't consciously pull the trigger. He says he was in a state of terror, believing an intruder was about to come out the door.

Dixon was not present during the autopsy and based his findings on photographs.

He contested the state's analysis that Steenkamp fell into a sitting position on a magazine rack after the first shot hit her in the hip.

South Africans were riveted by Nel's tough cross-examination of Dixon, with the forensic expert's name trending on Twitter.

The most retweeted tweet in South Africa on Wednesday came from standup comedian, Lazola Gola: "Did Dixon find this gig on Gumtree?" - a reference to a South African online classified advertising site.