Rod Drew on Lambton Quay in 1975, soon after graduating from police college at Trentham. The gear and kit is different now, Drew says, but basic policing skills are not.

Picture the veteran homicide detective – grizzled, gloomy, jaded after years dealing with humanity's worst, most hopeless cases.

The reality is remarkably different. Instead, Detective Superintendent Rod Drew is relaxed and cheerful.

Retiring this week after 42 years with the police, Drew is optimistic about humanity, about New Zealand, even about some of the crooks he's met.

ROSS GIBLIN/ FAIRFAX NZ Detective Superintendent Rod Drew leaves police after 42 years.

And he's dealt with some of the worst, investigating the deaths of Teresa Cormack, Coral-Ellen Burrows, and "Lillybing" Hinewaoriki Karaitiana-Matiaha.

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As he packs up or chucks out what he calls the "accumulated detritus" of that career, he's not entirely sure what's next for him.

kent blechynden Coral Burrows, 6, who was beaten to death by her stepfather Steven Williams after she refused to get out of his car and go to school.

He only turned 60 in February. Another job? Not right now.

He's just happy to leave with a clean slate – meaning no unsolved murders.

Retiring as national manager of criminal investigations, Drew says he found many criminals likeable, with irredeemable psychopaths a rarity.

"Lots of criminals, they're not inherently bad people necessarily, but they're people who make mistakes.

"I've also met some criminals who I don't like, who are evil people, but there are few of them."

Drew always wanted to be a cop. After leaving Rongotai College, he trained at Trentham.

As a cadet, he spent time with the Masterton CIB and a maximum security unit at Lake Alice Hospital.

By the time he graduated with 73 others, Drew and his mates were "police officers through and through".

He later worked in the car squad, fraud squad, drug squad, undercover programmes, and as Wairarapa area commander.

"In the old days, on the fraud squad, some of the old fraudsters were absolute characters. I mean, talk about good people skills.

"Coppers and criminals have probably been friends for a long time, on a working level anyway, because if you don't make friends with people as a detective, they're not going to tell you anything."

Drew's familiarity with the dark side of life hasn't atrophied his humanity either.

He dislikes discussing career "highlights".

What may be seen as a highlight for him will be someone else's tragedy.

New Zealand's most-decorated detective spent most of his career in Wellington, but travelled widely.

He doesn't keep count of the homicides, but they include many of the most horrendous, high-profile crimes against children.

He packs up during a week where the sickening death of Moko Rangitoheriri​ reignites child abuse debates.

Drew says the killing of James Whakaruru in 1999 really triggered the conversation.

"We had a series of cases that became quite high-profile, where the treatment of the child had been dreadful.

"Not just that the child had been beaten and killed, but the treatment, ongoing for a long time, had been dreadful."

Have the public conversations, media campaigns and national soul-searching made an impact?

Whakaruru's father Kevin Campus said this week Moko's death proved nothing had changed.

Drew has a different view, but admits changing familial behaviour is not easy. When he's been stonewalled, it's most often happened in gang-dominated communities, or during child homicide cases when families chose to close ranks.

He says increased rates of reported child abuse do not mean abuse is more widespread, but that people are less willing to ignore the mistreatment of kids like Moko and James.

These atrocities cut deeply for those investigating, Drew says, and require an often steely detachment.

"It's impossible not to feel very deeply for the families, but if you become emotionally involved, then there's the fear that you may not continue to be impartial and investigate in the way you should."

He says people who work with the grim, gruesome side of human nature need to learn when to switch off.

"You just have to learn that professional distance and if you do, there's a defence mechanism that springs up and protects you while you do those things.

"When there's a major crime, your life can change with a snap of your fingers.

"It doesn't matter if its your wife's birthday or your child's birthday or Christmas or anything else the following day. When it happens, you go."

Happily, Drew says New Zealand's a better, more compassionate place than it was in 1974.

But it's also a more complex place.

The growth of the internet and DNA science are part of that complexity, and have changed policing since Drew walked the beat in Wellington back when Norman Kirk was Prime Minister.

Cyber-criminals and paedophiles abroad can victimise New Zealanders, but can also be caught quickly, with the help of overseas authorities.

Drew says DNA enables breakthroughs, like the conviction of Jules Mikus​ for the murder of Teresa Cormack, another of his cases.

But it also requires a new level of meticulousness when police tiptoe around crime scenes.

But basics of good detective work remain, he says.

"The first thing you've got to do is like people. Because if you like people then you want to do good things for them."

Just as Kiwis were capable of changing attitudes to child abuse, Drew says maybe another debate is needed around the most common cause of preventable crimes.

A constant over 42 years, he says, has been the role of booze in making otherwise reasonable people do crazy things.

Drew says changing attitudes towards binge drinking will be tough.

He's wary of sounding like a finger-wagging hypocrite because many of us have done silly things on the booze.

But he says our casual attitude to getting hammered should probably be reassessed – for our own good.

As he shreds the documents and old crime scene photos he can't take home, Drew's close connection with police will continue.

His middle son Braden joined the force in 2014.

Will Braden become a detective too?

"It's entirely up to him but I think it's probably natural that he thinks that would be a good thing to do. But he's only 18 months in, so who knows."

The superintendent's cheery outlook may be encouraging for anyone planning a similar career path.

"I actually have a positive view of society and people, and I think we've got great promise for the future."

ROD DREW AT A GLANCE:

* Born 1956



* Went to Island Bay Primary School, South Wellington Intermediate, and Rongotai College

* Started in Wellington as a beat cop

* Went on to the position of detective superintendent

* Ran a number of high-profile murder investigations including those of Teresa Cormack, Coral-Ellen Burrows, and "Lillybing" Hinewaoriki Karaitiana-Matiaha.