More than half of all crimes in Britain's second largest police force area are not investigated, its highest ranking officer has confirmed.
Greater Manchester Police Chief Constable Sir Peter Fahy said his officers are only able to concentrate on around 40% of reported crime.
The admission comes against a backdrop of nationwide cuts to police spending, which will see force budgets taking a 20% hit in real terms by 2015.
Sir Peter, who is vice-president of the Association of Chief Police Officers (Acpo), said: "Most crime is committed by a group of active, persistent offenders who go in and out of the criminal justice system. So, in continuing to reduce crime, we balance between investigating offences after they have happened and targeting those who we know are out there every day, looking for criminal opportunities. Some of these we visit twice a day to keep them on their toes.
"In the same way that the health service concentrates on the most serious illnesses and the treatments likely to have most effect, the police have to concentrate on the most serious crimes and those where there are lines of investigation likely to produce evidence of the offender.
"In practice, this translates into about 40% of crime being actively pursued at any time. We look at all crimes to identify patterns of offending and to build the picture of where we need to target police patrols. In many crimes there are no witnesses, no CCTV and no forensic opportunities."
Greater Manchester Police needs to save £145.5 million over the four years of the spending review until March 2015, with a report by Her Majesty's Inspectorate of Constabulary (HMIC) this summer stating how the force had planned to cut police officer numbers by 19% over the five years to that deadline.
Over the first two years of the spending review, recorded crime (excluding fraud) fell by 19%. The figure for England and Wales is 13%, the report stated. Victim satisfaction remains high at 85.1%, which is broadly in line with other forces.
But in 2012/13, Greater Manchester Police received more emergency and priority calls from the public, and deal with more crime per head of population than other forces in England and Wales.
The report stated: "As a large organisation (GMP has) scope for economies of scale and a level of overall resilience, but driving major change and changing the culture of a large organisation is complex and demanding. The force had a strong response to the spending review challenge and has achieved one of the greatest reductions in crime levels in a force area over the spending review period."