The beating only stopped when a former colleague of Mr Higgs, who happened to be driving past at the time, urged him to get into her car.
The young man then allegedly used a knife to inflict several wounds on himself including, it is understood, puncturing a lung.
The man and his grandmother were both taken to Hawke's Bay Hospital and the teenager was later flown to Wellington Hospital in a critical condition.
Police said yesterday the man remained in Wellington Hospital's intensive care unit over the weekend but was due to be moved to a ward at the hospital yesterday.
It was likely he would be transferred back to Hawke's Bay Hospital sometime during the coming week.
Police said he would undergo a mental health assessment and a decision on charges would follow.