Eunji Ban was found dead in Wickham Park on the morning of November 24, 2013.

The trial of a man accused of the brutal murder of a Korean student in the Brisbane CBD has been abandoned after a jury found he was not mentally fit to continue.

Alex Reuben McEwan, 23, had pleaded not guilty to murdering Eunji Ban, despite formally admitting to killing her in the early hours of November 24, 2013.

The jury was told on the first day it was not contested Mr McEwan had caused the 22-year-old's death and determining his mental state at the time would be a key focus of the trial.

But in a twist brought on after two long delays sparked by the defendant’s “present state of mind”, the trial changed tack.