Davis said efforts to get further information had been difficult, with details not being sent from the prison.
An apology from Serco staff over an unrelated instance where an inmate's mail to an MP was opened and read had damaged confidence it would arrive if sent, he said.
Serco staff apologised to the inmate, who had written with concern about Serco's management of the prison and the safety of inmates. He also received an apology from the prison manager who asked him to change details in the letter.
Serco's prison woes are most closely tied to its failed management of the Mt Eden Corrections Facility, which cost the company $8 million in break fees after losing the contract.
The company came under scrutiny after footage emerged of "fight clubs" which saw inmates taking part in bare-knuckle brawls.
Serco also has the contract to manage the 960-inmate Auckland South Correction Facility at Wiri - a 25-year contract worth almost a billion dollars.
In a sequel to the inquiry which cost the company its contract, an investigation by the prisons inspector found a string of failures by Serco with the handling of the case of a French inmate.
Join French-Irish citizen Kevin Mussard has been left with life-long injuries after an assault which left him bleeding and unconscious. He suffered a fractured skull and 22 stitches.
The prisons' inspector found guards didn't respond quickly enough and one walked past Mussard as he lay bleeding. It also emerged the inmate had been beaten even though he had asked to be placed in segregation.
Mussard's lawyer Martin Hislop said it was likely a damages claim would follow, given his client was likely to carry the scars of his brief stay in prison for life.
"He's just trying to get his life back together. He's pretty scarred, he's an emotional wreck and it's just possible there's some brain damage. There should be some damages that should be pursued."
Hislop said his client should not have been in jail, having been refused bail and forced to wait in prison until his case was called.
A spokeswoman for Corrections confirmed the allegation had been made and was being investigated.
"Corrections has received this allegation and has referred it to the Corrections Inspector responsible for ASCF. The Inspector is expected to complete her advice to the Chief Executive shortly."
She said the Corrections Chief Inspector's investigation into the assault on Mussaud had found concerns over the way staff responded and record keeping over the inmate's request to be kept segregated from other prisoners.
Serco's reporting of assault during the year Mussaud was injured incurred a $50,000 deduction from its contract.
"Many offenders resort to violent behaviour as a means of resolving issues. Corrections does not tolerate prisoners using violence against staff or other prisoners, and any prisoners found to be using violence will be held to account for their actions," said the statement from Corrections.
She said Corrections was satisfied the issue relating to the inmate's letter had been handled appropriately by Serco. "Prisoners have a legal right to send correspondence to their lawyers and MPs without being opened. Corrections accepts this appears to be an isolated incident."
Serco prison director Mike Inglis said the company was "working with the Inspectorate team to provide information on our education assessment practices" at Wiri prison.
A Serco spokeswoman said three staff had written letters of apology to the inmate whose letter had been opened. "The Prison Director also wrote a letter of apology to the prisoner for this unacceptable breach of his legal rights."
The spokeswoman said Serco had also apologised for times its management of Mt Eden prison fell below standard. "We regret any incident of violence which resulted in injury to a prisoner."
She said the new men's prison at Wiri "has been operating well under our management". "We have a strong team there focused on delivering our services. We are determined to do well and learn from our mistakes in MECF."
The Herald is still seeking comment on the claims an inmate was passed answers to an exam.
