In today's Focus on Politics podcast, investigative journalist Guyon Espiner talks to a leading defence lawyer, the chair of the IPCA and the commissioner of police about whether the police watchdog is fit for purpose.

"We have police officers telling us things they don't tell police in the criminal investigations against them ... what they do tell us cannot ever be used against them," - IPCA Chair Judge Colin Doherty

The Independent Police Conduct Authority (IPCA) holds an important constitutional role in New Zealand as the only body to monitor the actions of the police.

The IPCA has completed investigations into 36 of the 39 fatal police shootings since 1990 and in every case has ruled the killings were justified.

But RNZ investigative series Licence to Kill found the IPCA has limited powers to hold the police to account and relies heavily on the resources of the police themselves.

Listen to the full podcast here

IPCA chair Judge Colin Doherty and Police Commissioner Andrew Coster

The IPCA was established in 1988 and only got its own independent investigators in 2003.

Now it has about 40 staff and a budget of $5 million a year, but its resources are tiny compared to the police's 14,000 staff and budget of $2.2 billion a year.

IPCA chair Judge Colin Doherty says the authority does not have the resources it needs to do the job the way he thinks he should be done.

He steps down from his five-year term in August, and says the IPCA of the future should be totally independent by answering to Parliament like the Ombudsman and the Auditor General, rather than to the government.

He says that would increase its independence from government, but a leading defence lawyer also questions whether the IPCA is independent from the police.

Read more:

Licence to Kill: The startling truth about New Zealand's fatal police shootings

How the police watchdog is more secretive than the spy agency

Shooting to wound 'something from the movies' - Coster

Police who killed were given evidence in advance

The Detail: Behind the story about secrecy in how we police the police

The IPCA only independently investigates 2-3 percent of the complaints it receives. Many of the others are simply passed back to police to investigate themselves.

Defence Lawyers Association co-founder Christopher Stevenson says that fuels a perception the IPCA is not genuinely independent - and a lack of transparency doesn't help.

Despite being a Crown Entity, the IPCA is not subject to the Official Information Act (OIA), which closes down a vital accountability mechanism for proper scrutiny.

Stevenson says open justice is essential to a free and democratic society…

Go to this episode on rnz.co.nz for more details