Tonkin has insisted in the past that his Penrich investment fund was a one-man-band.
The 15-week trial began with a challenge to James Hardie to find properties built with Harditex that don't leak.
RITANZ says it regrets how long the process took, but it needed further investigation.
The government has said it will upgrade its Licensed Building Practitioners scheme as leaky building issues come to light again.
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