The gruesome murder happened at the Pick 'n Save Superette in Klipfontein Road, next to the Saartjie Baartman Centre, in broad daylight on 9 October 2015.
Nikita, 24, had been at the centre for her safety following an incident on 19 August 2015 when Simbarashe threw acid in her face.
The court found that Simbarashe stalked her, waited for her and stabbed the woman 34 times.
Throughout the trial, Simbarashe had told the court he was mentally ill or that he could not recall or remember the violent episodes.
In a two-day judgment, Acting Judge Melanie Holderness said Simbarashe made up the evidence as he went along.
“There were marked inconsistencies in the many versions of his testimony. He fabricated evidence and much was being made up as he went along,” she ruled.
“He lies unapologetically. The accused relies on mental illness to defend himself, but there is no proof of mental illness following (consultation with) a panel of three psychiatrists.
“Contrary to the evidence of the accused, his actions were deliberate and well-directed. He was like a battering ram in his attempts to get to the deceased.
“He illegally gained entry to Nikita’s mother’s home, coming in through the back door to get to her. He beat (mom) Bonita Lewis twice and she required stitches in her ear. He threw (ouma) Hilda Isaacs against the kitchen cupboard and broke her wrist.”
Simbarashe was found guilty of assault with intent to cause grievous bodily harm on Nikita, housebreaking at their Kensington home, assault on Bonita and assault of ouma Hilda.
He was also found guilty of common assault and assault on two women (Farren Ben and Sherlock Smith) who had been with Nikita in the shop when he came for her.
As they tried to defend her, he threw one through a glass display in the shop, while he beat the other one to the ground as her small, terrified children clung to her.
“The deceased made the fatal decision to run to the back of the shop. The witness (Smith) says he was sitting on top of the deceased and she screamed as she fought him off,” Holderness said.
“The accused cannot remember this incident and says he woke up at Manenberg Police Station, his yellow top covered in blood and was told he had killed someone.
“This court is satisfied that the State has proven its case beyond a reasonable doubt. I am of the view that the accused had full cognitive control at the time of this brutal and senseless attack.”
Simbarashe looked earnest in court and showed no emotion as he was found guilty.
Outside court, a smiling Bonita expressed relief at the outcome.
She said: “I was confident that he would be found guilty and I am grateful that the judge is gonna put him away. That is all I want. Nikita had her problems, but she never deserved to die so viciously. I just wanted today to be finished.”
Sentencing proceedings are set to start on 4 March.