Alex Fisher's older brother was back in court yesterday, charged with murdering the 10-year-old, a prosecution that could hinge on mental health assessments.

Eric Baden McIsaac, 25, Masterton, appeared in the High Court at Palmerston North as his family looked on from the public gallery.

His lawyer at the court, Letizea Ord, and Justice Simon France, streaming live via an audio visual link from Wellington, discussed the next steps in the court process, under mental health legislation.

The judge said McIsaac's fitness to stand trial will be assessed.

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Alex's body was found on Waitarere Beach, near Levin, on October 8 after his disappearance sparked a huge manhunt.

During the search, police released CCTV footage showing Alex and McIsaac together in a store on October 5.

Court documents show McIsaac allegedly killed Alex either that night or the next day.

McIsaac is also charged with unlawful possession of a knife in a public place and burglary.

He is yet to enter pleas to any of those or a fourth charge, which is suppressed.