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Auckland police are looking for two youths seen throwing rocks off a motorway overbridge at cars passing below.
The pair, described as school aged, were seen on a bridge over the Southern Motorway near Manukau.
One of the rocks narrowly missed a windscreen but hit the underside of the car. The driver called police, but by the time officers got to the bridge, the teenagers were gone.
A source said several other cars were also hit and forced to stop this week on the motorway, which has a speed limit of 100km/h.
In 2005, Chris Currie, 20, died when an 8kg concrete slab was dropped from the Princes St overbridge, not far from the bridge in Manukau.
He was driving his girlfriend, Helen McCreadie, and two other passengers from Taupo to Auckland at the time of the tragedy.
The concrete that smashed through the window of the car on to Mr Currie broke his jaw and shattered his sternum, driving it into his heart.
As he slumped in the driver's seat, Ms McCreadie tried to control the car. It crashed after 200m.
In 2006, Ngatai Rewiti, 15, was jailed for four years for Mr Currie's manslaughter. Just 14 at the time of Mr Currie's death, Rewiti was initially charged with murder but a jury found him guilty of the lesser charge.
A month after Rewiti was jailed, a rock thrown from a Tauranga expressway overbridge smashed through the rear window of a Toyota station wagon. The couple in the car were shaken but not injured in the "extremely dangerous attack".
A police spokeswoman said the latest incident was being investigated. It followed reports of similar incidents several weeks ago.
"Throwing solid objects off motorway overbridges is a potentially very dangerous activity," she said.
"Young people might not be aware of the seriousness of this ... but we'd like to convey to them that throwing anything into the path of a moving vehicle could result in a car crash which can cause serious injury."
Meanwhile, pieces of a car being driven by 22-year-old Rutger Hale when he was killed after a mystery object smashed through the windscreen are to be sent to forensic experts in Auckland for analysis.
The Aucklander died on October 24 as he drove up the Maungawera Hill near Wanaka with his partner, Danielle Oylear.
The mystery object has not been found despite extensive road searches and a public appeal.
Police said yesterday that they had been talking with "a number" of drivers of white utes, after Ms Oylear - who was in the passenger seat - reported seeing such a vehicle travelling past in the opposite direction about the time the object came through the windscreen.
Officers said they remained "very keen" to hear from the driver of a vehicle towing a fishing boat which pulled over at the top of the hill to let a white ute past, as well as any other drivers who were in the area.