A post mortem examination was conducted on Monday to establish a cause of death, the statement said.
But the results were inconclusive and further tests will now be conducted over the coming weeks.
Millerchip pleaded guilty to assaulting the pensioner causing him actual bodily harm and was due to appear in court later this month for sentencing.
But due to Singh's death detectives have notified the Crown Prosecution Service (CPS) and will await a decision over what further steps may need to be taken.
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