In actual fact, he may not not be retried. Perhaps only resentenced.
The guilty verdict was confirmed by the appeals court. However it was the sentence that was not upheld as a result of contradictions in the justification for the sentence (as far as I understand). It has something to do with a "subconscious latent readiness to kill" and the appeals court considered this a contradiction in terms. It also felt that the comment by the original court that the defendant was "consumed by revenge" was arbitrary and not based on any facts. The State Prosecutor felt that the appeals court was being pedantic and regretted the appeal.
As there are still two appeals to other courts pending, it is as yet unsure how things will develop and what the next steps will be.