A former tutor at the University of Otago told police he killed his ex-girlfriend because of the emotional pain she caused him.
Clayton Weatherston, 33, is charged with stabbing student Sophie Elliot at her family's home in Dunedin in January last year.
Mr Weatherston denies murdering Miss Elliot, 22, but has admitted to manslaughter.
The defence says Mr Weatherston was provoked by Miss Elliott attacking him with scissors, and by the pain their tumultuous relationship had caused him.
Miss Elliot died after she was stabbed or cut more than 200 times.
On Tuesday the jury heard evidence from Constable John Cunningham who was first to reach Miss Elliot's family home after her mother called police.
Mr Cunningham told the High Court in Christchurch he found Mr Weatherston standing near Miss Elliot's blood-stained body.
When he asked the accused what he had done, Mr Weatherston replied in a calm voice: "I killed her".
Mr Cunningham told the court Mr Weatherston appeared to be in control of himself and said he killed Miss Elliot with a knife and a pair of scissors because of the emotional pain she had caused him over the past year.
The Crown is nearing the end of its case.
