DNA belonging to Rudi and Teresa van Breda was found under triple murder accused Henri van Breda's fingernails and in a corner of the shower, the Western Cape High Court heard on Monday.
No unknown DNA was found in the family's luxury De Zalze Estate home.
The 22-year-old's trial resumed more than a month after proceedings were adjourned with the testimony of Lieutenant Colonel Sharlene Otto, the police's chief forensic analyst.
She also confirmed that Henri, Teresa and Rudi's blood was found on the floor in the corner of the shower.
Strict and stringent quality control systems were in place and the laboratory was guided by international standards, Otto said.
Van Breda pleaded not guilty to axing his parents and brother to death, seriously injuring his sister Marli, and defeating the ends of justice.
He claimed that an intruder wearing a balaclava, gloves and dark clothes was behind the attack, and that he had heard other voices of people speaking Afrikaans in their home in the De Zalze Estate in Stellenbosch in January 2015.
Van Breda claimed that, after a fight with the axe-wielding intruder who was also armed with a knife, the man had escaped.
Otto said Martin's right-hand nail scrapings showed Rudi's DNA, while a swab taken from the handle of the knife used in the attack - which comes from the family's kitchen - only matched Rudi.
A total of 216 samples were submitted from the scene, far more than what they would usually receive, she explained.
When asked by State prosecutor Susan Galloway what the odds were of a person entering a space and not leaving any DNA, Otto said someone covered from head to toe wouldn't leave behind a trace.
She also explained the Locard principle - that every touch leaves a trace. "That is a first law of forensics," Otto said.
Advocate Pieter Botha, for the defence, is expected to cross examine her on Tuesday.