The private company entered its plea in the Kalgoorlie Magistrates Court on Thursday and sentencing is scheduled for June 3.
The elder - who cannot be named for cultural reasons - died of heat stroke in the back of the un-airconditioned van while being transferred from Laverton to Kalgoorlie in January 2008 to face a drink-driving charge.
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G4S was charged under the Occupational Health and Safety Act with failing to provide reasonable care to ensure the health and wellbeing of a person in its care.
The company faces a maximum penalty of $400,000.

