Department of Labour communications adviser Colin Patterson said yesterday no cause had been found, and the six-month period in which a prosecution could take place had passed.
The incident occurred on June 17 last year, when the crane narrowly missed a bus full of 6 and 7-year-olds after the bus driver stopped just centimetres from the crane.
No-one was seriously hurt in the incident, which happened after the mobile crane, owned by Dunedin Crane Hire, had lifted a cooling tower to the top of the Dunedin Hospital ward block.
Mr Patterson said the investigation was continuing, but no cause had been found yet.
"Under the Health and Safety Act, we have six months to prosecute.
"That six months has passed."
He said the crane was not operating, and would not do so until a suitably qualified person had given approval for it to be used.
"When, or if, that will happen, I don't know.
"It's a highly complex piece of machinery.
"We're trying to get to the bottom of it."
There was no deadline for the investigation to end.
Rather, it would "continue for as long as it needs to", Mr Patterson said.
The Otago Daily Times informed crane owner Doug Hall of the Department of Labour's decision, but he declined to comment on it.
However, he said a new boom had been built for the crane and was being sent from Japan.
He hoped the crane would be back in operation within the next two months.
