They call it "silent running" or "creeping". Driving through city streets without emergency lights, siren or - maybe - headlights, the better to catch criminals.
Whether this happened on the night of October 15, 2009, is a point of contention. But one thing is sure. Just after midnight, a patrol car, manned by two Los Angeles Police Department officers, received radio reports of two separate burglaries in the city's Venice district.
The second report said thieves were apparently still on the premises.
The Ford Crown Victoria - the standard LAPD "black and white" cruiser - raced down Venice Boulevard, its siren and emergency lights off, intending to provide back-up.
Thereafter, events are contested. But the outcome has shone a critical light on the LAPD's flawed driving record, in a sprawling city where cruisers are vital for a fast crime response, and cost city taxpayers millions of dollars.
According to James Eldridge, the LAPD veteran who was driving, a BMW sedan suddenly emerged from a side street.
Unable to stop, the patrol car crashed into the driver's side of the BMW, which spun around as the Ford hit a tree. Eldridge and his partner, Ramon Vasquez, received minor injuries. The BMW's driver, Devin Petelski, 25, who was heading home from work, died in hospital from her injuries.
The police blamed Petelski.
When a rumour began that the officers had been silently running when they hit Petelski, the LAPD was quick to rebut "erroneous information". Tests proved the cruiser's headlights were on. Eldridge estimated his speed at 65km/h to 72km/h.
The LAPD's Specialised Collision Investigation Detail studied skid marks and the vehicles' weight, and settled on 78km/h.
Investigators also said they were unable to recover data from the cruiser's "black box", a computer that records speed and braking for just under half-a-minute before airbags inflate. But the attorney for Petelski's parents, who had filed suit against the department, had better luck.
A report in the Los Angeles Times said data showed the cruiser had almost stopped, then abruptly accelerated before impact, climbing from 50km/h to 120km/h in 10 seconds.
It hit the BMW at 125km/h. This was backed up by independent analysis acquired by the Times. Eldridge stuck with his story and the LAPD insisted 78km/h - at which the department claims siren and emergency flashers are not needed - was the true speed. It said Petelski caused the collision.
Nonetheless, in April 2010, the plaintiffs received US$5 million ($6 million) in an out-of-court settlement, the second-highest amount ever paid by Los Angeles in a crash involving its officers.
This is not a sustainable solution to such incidents.
Last week, the Times reported LAPD officers "were involved in traffic accidents more than 1250 times in the past three years - an average of about one a day".
Many were minor. But others, like the Petelski case, were serious. Almost US$24 million has been paid to settle litigation in 400-odd LAPD crashes in the past nine years.
The paper, which posted city accident statistics on its website, said "dozens" more cases await settlement.
Tellingly, the city opted to settle "all but a few" of the resolved cases rather than take its chances in court, "a strong indication that the officers were in the wrong".
This may come as a surprise to addicts of fast and furious TV shows or video games featuring LA's Finest - motto "Protect and Serve" - where the most excessive driving can seem mercifully risk free. Reality is very different.
"We've had several of those cases, too," says Paul Zuckerman, a Beverly Hills attorney who has spent two decades litigating them. "Where the officers are travelling at extremely high rates of speed in violation of the rules.
"Now the California Vehicle Code says that if any officer is responding to a Code 3, then they are allowed to basically violate the rules of the road as long as they are not grossly negligent. A lot of times though, in Code 3, the police driver has been authorised to put the sirens on and activate the lights. Then they're given the protection of the Vehicle Code, which says that they shall be relieved of any responsibility unless they're driving in a grossly negligent fashion. Otherwise they have to follow all the rules of the road, just like a private citizen."
That's the rule book. But Zuckerman says it can go out the window on LA's mean streets.
"Frequently officers hear things on the radio, like 'shots fired' or 'officers needs assistance'. And they decide to go to the scene and travel at high rates of speed without being authorised by Code 3. And that was the case with the US$5 million payout. The officer was not permitted to respond Code 3, but accelerated from 80km/h to almost 130km/h in 15 seconds and killed that girl."
There may be several explanations for this. Police officers are trained for high-risk situations and LA's gang land can be very high-risk indeed. Nonetheless, blood can be up, especially if there are fears a comrade is in trouble.
And then there's "creeping".
Zuckerman says police deny doing this. Nonetheless, many believe that cruisers sometimes "creep" gang or drug-infested neighbourhoods - and parts of Venice not far from the Petelski crash site have an unsavoury reputation. "They try to catch the bad guys," says Zukerman. "And they may fail to turn their lights back on at night when responding to a call."
In some ways it seems miraculous that the LAPD can negotiate the often gridlocked city at all; hence the rule that traffic pulls over to let emergency vehicles pass.
The LA Police Commission has pledged to enact safety measures. The department is also pondering whether to give traffic deaths the same priority as fatal shootings by police, where officers involved are separated after an incident to prevent them fabricating a cover story.
In 2008, the LAPD instigated a penalty system for offenders, using a sliding point system. Three points in 24 months means the offender must take a "standardised driver improvement training course".
Five points in 36 months draws a six-month suspension from driving. And eight or more points, or four preventable accidents in 36 months gets offenders transferred out of the department.
It is unclear if this system has improved driving in the LAPD.
The Times' Joel Rubin, who investigated the LAPD's crash rate, found that although accidents had declined a little since the point system debuted, claims against the department had risen 40 per cent since 2008.
This record would seem to buck national trends.
According to the US Department of Transportation, road deaths in 2010 fell for the sixth straight year and reached their lowest level in 60 years, with 32,885 fatalities, even though Americans clocked up an extra 46 billion miles since 2009.