Hunt to find out if security guard who walked in on Brown and Chuang was silenced.

The investigator probing Auckland Mayor Len Brown's tryst with his mistress in the council's Ngati Whatua room was concerned the security guard who'd walked in on the lovers was muzzled.

Emails obtained under the Official Information Act reveal the Ernst and Young fraud investigation boss suspected the guard - who unwittingly caught the mayor and Bevan Chuang having sex in a council room - may have had "pressure bought to bear on them to keep quiet".

Chuang revealed the interruption when she disclosed the affair last year. Efforts to identify the male guard - one of 16 to have worked during the past few years at the Town Hall where the Ngati Whatua room is located - were fruitless.

An email on November 7 last year from the council employment relations manager Andre Lubbe to security manager Dean Kidd indicated there was "some suspicion" about one guard.


Lubbe named him in the email but his identity was redacted in papers obtained by the Herald on Sunday.

Nearly three weeks later, the mystery of who interrupted the lovers early in 2012 deepened.

EY's fraud investigation and dispute service senior manager Matthew Hammond assured council staff EY was not concerned about their actions or inaction but whether the guard had been silenced.

This included any "inducement or coercion" to keep quiet.

Hammond wrote to Kidd asking to speak to them as a group at handover briefings at the end of their shift rather than scheduling 15-16 separate interviews.

The EY review eventually cleared Brown and Chuang of any coercion, finding they neither knew the identity of the guard nor sought him out after the incident.

No correspondence in council email data was found relating to the security guard and management at The Edge, who oversaw security for the Town Hall, were not able to identify the guard.

Mayoral office spokesman Dan Lambert declined to comment about the hunt for the guard but said an extensive investigation cleared the mayor of inappropriately using council resources.

Details of the two-year affair came to light last October, just days after Brown won a second consecutive term as mayor.

The $100,000 EY review found Brown did not inappropriately use council resources to support the relationship.

However, the review found Brown received nine free hotel rooms during the review period, including one spent with Chuang. He also used the council-provided phone to make 1375 calls and texts to Chuang.

The lengths they went to

• The Ernst and Young (EY) investigators sought a massive amount of information in the Brown inquiry:

• Footage was requested for three years from security cameras posted around the Auckland Town Hall, including the entrance and exit around the Mayoral offices.

• 470,000 relevant records of up to 200 GB of data was extracted from staff emails between November 2010 and October last year. A council spokesman said this amounted to more than 11 million staff emails forensically searched by investigators.

• Three female staff members in the Mayor's office were asked to provide privacy waivers to allow checks about bookings made for the Mayor at the Hilton, SkyCity and the Langham hotels.

• Six of the 25 telephone numbers with the highest frequency of calls and text messages from Len Brown's phone could not be attributed to a person or company. One of the frequently called numbers belonged to a woman in the mayoral team. The rest were not on the council's Vodafone or Telecom accounts.

• Chief executive Doug MacKay warned EY to give Brown access to all details to lessen the chance of successful legal proceedings. Lawyers for Meredith Connell told McKay it was important Brown had access to the detail behind any contentious issue, including emails and conflicting records.