Greater Manchester Police wrote off nearly 300 rapes and 9,000 house burglaries in the first six months of last year as unsolved.
The force logged 86,211 crimes in total as 'investigation complete; no suspect identified' from January to July 2019.
The figures were released after a Freedom of Information request by the Liberal Democrat MP, Layla Moran.
She said it was "scandalous" that so many cases were closed unsolved.
But GMP's Assistant Chief Constable, Rob Potts, said that at a time of "reduced resources and more demand" officers had to make "difficult decisions" every day to ensure they were protecting the most vulnerable.
The figures revealed that 284 rapes and 317 drug trafficking offences, 2,788 stalking and harrassment cases, and 8,922 residential burglaries were not solved in the period in Greater Manchester.
In addition, also unsolved were:
*3,091 business and community burglaries.
*12,015 criminal damage and arson attacks.
*689 other sex offences.
*586 possession of weapons.
*1,983 robberies of personal property.
*5,428 shoplifting offences.
*14,583 vehicle offences.
*3,222 violence with injury offences.
The MP discovered that in total throughout the north west 181,050 cases were unsolved after compiling figures from GMP, Cheshire, Mereseyside and Cumbria Police for 2019.
Two thirds of burglaries and vehicle crimes were closed.
Nationwide there were 68,848 stalking and harassment cases, 2,632 drug trafficking and 4,637 weapon possession offences where no suspect was identified before the case was closed.
Screening out crimes, in which a police force marks a case as requiring “no further action”, has increased rapidly over the last decade and grew from 361,180 in 2010 to 2.2m last year, equivalent to 43% of all crimes.
Where something was stolen from a vehicle, police failed to identify a suspect in 93% of cases. Ms Moran even uncovered a murder was logged as case closed by South Yorkshire Police.
The MP said: "It is scandalous that we are seeing so many crimes in the North West are closed without further investigation by police forces. It's imperative that the police explore every avenue and act with compassion for the victims and their families when investigating these crimes.
"We are seeing murders, rapes, stalking cases and serious assaults filed, nothing happening for months, if at all, and reports just gathering dust in a police filing system. All the while victims are longing for justice.
"It is also vital that decisions made by the police about investigations, and the reasoning behind their decisions, are clearly and fully communicated with victims so they do not feel they have been left in the dark.
"At the moment millions of people are left without justice and rightly angry that criminals are getting away scot-free ."
Assistant Chief Constable Rob Potts said: “Being a victim of any crime can have a devastating impact on the lives of those affected and their families and communities. We work closely with victims to support them through investigations and update them with the progress and the eventual outcomes.
“In many incidents, if there are no witnesses, CCTV or forensic opportunities, this means there are no leads for officers to investigate further. Where evidence is present, officers will investigate proportionately and we rely on the public to help us do this by reporting suspicious activity.
Get the latest updates from across Greater Manchester direct to your inbox with the free MEN newsletter
You can sign up very simply by following the instructions here
“If certain investigations are not continued following an initial assessment, this does not mean that no positive action is taken. There’s lots of different support available for victims of crime aside from the investigation including the Victim Services Partnership in Greater Manchester which helps to support and signpost those who need specialist support.
“It’s vital that people report crime to us so that we can consider the overall picture of criminality when targeting offenders and crime hot-spot locations. We are committed to continuing to work closely with our partners and all communities to problem-solve within neighbourhoods in order to prevent crimes reoccurring.
“Protecting the public from harm will always be our top priority. At a time when we have reduced resources, more demand and more complex and serious crime, we have to make difficult decisions every single day to ensure we are protecting our most vulnerable and assessing the threat, risk, harm and vulnerability posed by each incident. The cases which are deemed the highest in terms of those priorities are where our resources must be focused.”