An electrical expert says data from what was effectively the black box of the Pike River Mine was "critical" to the investigation.
His comments come after police admitted they didn't look at the black box beyond the first explosion.
Some Pike families say this was negligent because the second explosion changed everything - ending the rescue operation and all hope of finding any of the 29 men alive.
Electrical expert Richard Healey told The AM Show on Thursday the families had been chasing the information for nine years.
- Pike River re-entry 'beginning of the end of a journey'
- Pike River recovery teams encouraged despite nothing of interest found
- Pike River timeline: From the first explosion to the re-entry
"It's critical to the investigation," he said.
On November 24 2011, five days after the first explosion, time ran out for any possible survivors and their families with the devastating second explosion.
Since then, Pike families have been keen to know what happened between the two explosions. It turns out there is a way to find out - it's called SCADA data.
"The families have sat through a Royal Commission," Healey said on Thursday. "All the way through the families have simply wanted answers to simple questions."
SCADA monitors all the cameras, the communications, the pumping stations, the gas and fluid levels and the electrics. It holds all the clues to what causes mine explosions.
The head of the Pike investigation, Det Spt Peter Read, said the police were concentrating on that first blast so the data after that was of no relevance to them.
Healey said it was "stunning".
"It keeps me awake at night," he said. "My heart goes out to the families - they've had nine years of this, it's just a cruel trick to play on the families."
He said SCADA was the "go-to" for any investigation.
"It's the go-to because it's machine-gathered information, it's not subject to human perception, it's not subject to failing memory.
"It is exactly like the black box on an aircraft."
One theory is that turning on a conveyor belt sparked the second blast. SCADA data could prove that one way or the other.
"It's beyond belief," Healey said.