A public inquiry is investigating allegations that some councillors, including flamboyant former deputy mayor Salim Mehajer, were making planning and development decisions to benefit themselves or their families before the council was sacked in February.

The public inquiry into the allegedly corrupt decisions of Auburn councillors has been summarised in one question: “How was this allowed to happen?”

The question was posed by new administrator Viv May as he took to the witness chair and described his takeover and review of planning decisions of the now merged Sydney council.

The inquiry is investigating allegations that some councillors, including flamboyant former deputy mayor Salim Mehajer, were making planning and development decisions to benefit themselves or their families before the council was sacked in February.

At the inquiry’s opening, counsel assisting the commissioner Paul Bolster detailed a litany of council decisions that would be examined.

These included the upgrading of a zone at Berala Village, which included property owned by councillor Hicham Zraika.

Councillors used colouring pencils to show how they wanted to rezone the area at a meeting in February 2014, the inquiry heard.

Mr Zraika declared an interest in an area to be rezoned and abstained from the meeting, where by apparent “coincidence” three councillors proposed a rezoning that would allow for an increased building height and further development on his land, Mr Bolster said.

A decision reflecting these three coloured maps was later maintained.

“How this happened … will be a focus of this inquiry,” Mr Bolster said.

The relationship between councillors and staff, including the now planning manager Glen Francis, will also be examined.

Councillor and former mayor Ronney Oueik arranged for tradesmen to renovate Mr Francis’s kitchen in 2006, but when the planning staffer came to pay a tradesmen for the cupboards, he was refused.

The $2000 cupboards were an undisclosed “gift” from Mr Oueik who “wanted to help the family out”, the hearing was told.

Mr Francis said the gift did not affect his subsequent planning decisions, some of which benefited Mr Oueik, the inquiry heard.

The inquiry will also examine the council’s response to the closure of a street for Mr Mehajer’s extravagant wedding at nearby Lidcombe last year, and other decisions including the approvals surrounding the construction of a faulty unit block developed by Mr Oueik in Lidcombe.

The apartment block, which had its roof ripped off during a January storm, was found to have significant structural defects.

The inquiry was told an application to modify the building’s roof had been approved by the council despite no application for a construction certificate.

Mr Francis said this was an oversight and he admitted the error, the hearing heard.

Insurers of the apartment block declined in April to accept liability for the damage, saying the building should never have been certified by the council.

“This is the human cost of what went on at the Auburn Council,” NSW Opposition Leader Luke Foley said outside the inquiry.

He rejected suggestions that the allegations justified the NSW government’s amalgamations policy.

Auburn Council has been carved up and folded into neighbouring councils under forced merger plans announced by the NSW government earlier this month.

But Commissioner Richard Beasley SC said, in his opening address, the inquiry will be conducted as if the council still existed.