Police Ten7 host says viewers are still playing a crucial role in cracking cases.

A man who caused a crash that killed a mother on her way to a wedding was among at least 582 alleged offenders who have been arrested thanks to Police Ten7. He was charged when a relative dobbed him after watching an on-screen appeal from police for information.

His dangerous driving had triggered a series of events that led to the 47-year-old woman's death on Auckland's Southern Motorway on April 26, 2013, about 4.15pm.

The man, driving a dark four-door sedan, had pushed into another lane in front of a Mazda, causing the second car's driver to have to take evasive action to avoid crashing into the barrier.

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The woman driving the Mazda lost control and hit the van the victim and her family were travelling in, which violently rolled and flipped over a concrete barrier, landing on its roof.

The mother in the van died instantly.

All police had to go on was grainy CCTV footage and investigators had "nearly exhausted" lines of inquiry when the case featured on the TV show on July 13, 2013, Police Ten7 host Detective Sergeant Rob Lemoto said.

However, the day after the broadcast a man called the 0800 TEN 7 INFO line to dob in a relative who had acted strangely when the pair were watching Police Ten7 together - jumping up and pulling the TV's power cord out of the wall when the crash item came on.

The caller said the family member, a 20-year-old man, had previously spoken about being involved in a crash.

The driver was arrested the next day and confessed to causing the crash.

He was convicted of dangerous driving causing death and injury and failing to stop and ascertain injury and was sentenced to two years' imprisonment.

The case illustrated how Police Ten7, which has aired on TVNZ 2 since 2002 and will celebrate its 550th episode on Thursday , helped police solve real crimes.

It may be one of the channel's most popular programmes but it wasn't onscreen purely for entertainment.

"We're actually catching people," Lemoto, who has been in the police force for 21 years, said.

"We normally put things on the show because we need the public's help. We genuinely need leads from the public to continue with the investigation."

He estimated that the number of arrests made as a result of cases appearing on the show was actually much higher than 582 because sometimes police in the field didn't have time to give Police Ten7 producers feedback about how information from viewers helped them solve a crime.

Information from tipsters also helped build cases that lead to another 332 arrests.

Many of the alleged offenders were caught after a friend or family member - usually a mum, dad or aunty - saw them on Police Ten7's "most wanted" segment or identified them as being the person responsible for the "crime of the week" and contacted police.

Others handed themselves in after being profiled on the show.

One young man was watching Police Ten7 with his dad in 2016 when he appeared as a "wanted face" on the show. His father packed him a toothbrush and spare pair of underwear and marched him off to the local station to spend the night in the cells.

Lemoto said people often reported their loved ones - who were sometimes committing crime because of drugs problems or bad environments - because they wanted to get them help and the only way to do that was through the police.

"It's not because they want to see them in trouble, I don't think anyone wants to get a family member or a friend in trouble.

"Sometimes we're the last resort. Some family members don't even know because they haven't had contact with these people for a while, so when they see them on the show as wanted sometimes it's the first time that they're actually aware they're in that kind of trouble."

He put the show's popularity down to viewers' curiosity about what was going on in their communities.

"New Zealand is full of good people who don't actually see a lot of what happens after dark or what happens on the police frontline, so there's that interest in it. To walk in the shoes of a police officer is still interesting."

Even after a long career in the force, things still surprised Lemoto, whose day job is in child protection in the Bay of Plenty.

"You think you've seen a lot but then every other week there'll be something that just makes you laugh or you're a little bit in disbelief."

Police Ten7's highlights
• At least 582 arrests have been made as a direct result of the show
• Information provided by viewers also helped police build cases that lead to another 332 arrests, so in total information indirectly or directly helped make 914 arrests
• 2423 serious cases and "wanted faces" profiled
• Season 22, which aired in 2015, was the most successful to date, directly leading to 79
• Footage of police officer Sergeant Guy Baldwin telling an alleged car thief eating a meat pie to "always blow on the pie" went viral in 2009 and made international headlines
• Information from several callers has helped police investigating the murder of Tirau woman Roma James after an appeal to the public about the case aired on Police Ten7 last month