Senior officers in Glasgow, despite success in reducing the number of muggings, say they are wasting their time investigating attacks which did not take place.
The city centre's police commander, Chief Inspector Martin Cloherty, said: "We have had cases where teenagers who have maybe lost their phone go home and say they have been robbed and suddenly that is reported to us.
"It is time-consuming but we can quickly discover using CCTV they were not actually robbed in the place where they said they were."
Police are now cutting such provably false incidents from their official statistics – helping to bring down their totals.
However, a new squad of officers, using detective techniques usually devoted to murders, is having an even bigger impact on muggings, senior officers said.
There were 676 robberies or assaults with intent to rob within city limits in 2011-12, almost two a day.
However, this compares with 1264 in 2006-2007 and 787 in 2010-11. This crime category includes everything from heists at bookies to street robberies, the police name for muggings.
The dramatic fall in those crimes – the vast majority of which are street attacks – comes after then Chief Constable Steve House last year warned of a spate of assault-and-thefts on people displaying iPhones in the street.
Val Thomson, the chief superintendent for Glasgow's A division – which covers the city centre – said: "People who commit robberies consider it to be quite a low-level crime. But the impact that has on a victim is horrendous."