The Ministry for Primary Industries was investigating the deaths, and it has now asked for the opinions of Crown lawyers.
"This matter is still undergoing legal review by the Crown solicitors and we are awaiting their recommendations," a spokesperson said.
At the time of the deaths, MPI's compliance director Gary Orr said if there was culpability, they would take action.
Orr said the ministry was not immediately told of the deaths, and only found out after it was tipped off by someone else.
"We were made aware of it through a third party, and it was only after we were provided that information [that] we reached out to the company and they then confirmed. That's going to be part of another conversation we'll be having," Orr said in December 2019.
Tegel confirmed the deaths were on a farm that it contracted to grow chickens.
"Tegel has confirmed that a power interruption on the grid and the subsequent failure in the backup systems has resulted in the loss of birds from a farm in Helensville. Tegel is working closely with all its contracted growers to ensure contingency systems are in place and working correctly," a statement said at the time.
Direct Animal Action spokesperson Deirdre Sims said no one should be able to kill hundreds of thousands of animals and get away with it.
"It's absolutely disgusting but unfortunately it's not surprising when you have companies like Tegel that cram thousands of chickens into these factory farm buildings.
"Tegel absolutely need to be held accountable for this."
