Police can spend weeks, months or even years scrutinising every line of enquiry to catch who they firmly believe the perpertrator is.
Someimes they do and they go to prison. But sometimes they are found not guilty and sometimes, they don’t catch anybody.
In Northamptonshire, the murders of 26 people remain unsolved - but police say they will never give up in their quest for justice.
Detective Chief Superintendent Kate Meynell, head of crime, intelligence and public protection at Northamptonshire Police, said: “The murder of a loved one has a devastating impact on those left behind and we do all we can to find those responsible and help secure a conviction at court.
“Despite our best efforts, there are times when there is insufficient evidence to arrest and charge a person in connection with a murder, or a jury returns a not guilty verdict.
“These cases remain open and are reviewed regularly to establish if there are any fresh opportunities for us to investigate.”
The unsolved murder cases in question stretch back to October 25, 1952 - almost 60 years ago.
In the sleepy village of Ashton, near Oundle, popular gamekeeper George Peach (64) and wife Lillian (67) were beaten to death in the middle of the night at their home.
More than 100 men were questioned, but police could not make anything stick and the story gradually disappeared from the front pages.
No matter how old the investigation is, police will look into any new information.
Det Ch Supt Meynell added: “Any new information is responded to and we will pursue any lines of enquiry available to us.
“This can be as a result of advancements in forensic techniques or because we have received new information.
“We will never forget those people who have had their lives taken away at the hand of another and remain committed to seeking justice in those cases that remain unsolved.”
One instance where new information could have led to a conviction in the county was seen earlier this year at Northampton Crown Court.
Pet shop worker Arthur Brumhill was found dead in the basement of his Northampton shop in March 1993.
Stuart Jenkins, who worked at the shop for a month prior to Mr Brumhill’s death, was arrested at the time but was released.
He was then re-arrested and charged in 2015 after new forensic information, but was found not guilty after a trial.
But some families don’t get that close to the justice and closure they so desperately desire.
One of the biggest murder investigations in the north of the county involved the disappearance of Kettering teenager Sarah Benford, who went missing from a care home in April 2000.
It has been treated as a murder since 2003 and last year, police searched an area of woodland near Kettering ahead of what would have been her 30th birthday.
Despite pursuing more than 5,000 lines of enquiry making eight arrests, police have never solved the case.
Speaking last year, Sarah’s mum Vicky said: “As a family we are looking for closure around her disappearance and somebody must know something.
“We would ask for people to contact the police if they know anything about Sarah’s disappearance.
“As a family we need to come to terms with what has happened and won’t be able to do this until we know what has happened to Sarah.”
Other significant investigations which have recently passed a milestone include the death of three-year-old Callum Bland.
Callum died after an arson attack outside his home in the Hemmingwell estate in Wellingborough in March 2007, but despite arrests nobody has ever been charged.
Two well-known local figures were also murdered in separate attacks in Wellingborough and Corby.
In August 2011, 76-year-old Hungarian Karoly Varga was repeatedly struck in the head with an ‘axe-like’ weapon at his home in Cannon Street, Wellingborough.
Elemer Patakfalvi was arrested and charged but the CPS dropped the case against him. Mr Varga’s killer has still never faced justice.
Then, just three days before Christmas in 2012, Corby nightclub owner David ‘Les’ Ross was killed in a hotel by a blow to the head.
Many were arrested, but nobody was ever charged with the killing.
Fast forward to recent years and three murder cases from 2015 still remain unsolved in Northampton.
Jon Casey was stabbed in Barrack Road in January, but suspect Waijs Dahir is believed to have fled the UK.
The remains of Adeyemi Olugbuyi - known as ‘Big Man’ - were found by litter pickers in Billing Brook Road in June.
He was reported as missing since September 2013, but despite a number of arrests nobody has ever been convicted.
David Brickwood was 74 at the time of his death and is the county’s most recent unsolved murder.
Mr Brickwood’s life was brutally cut short at his home in Linsday Avenue in September when raiders burst in and delivered a devastating assault.
Speaking after his dad’s inquest in May this year, son Dale said: “I just want the people responsible for this to be brought to justice.
“I won’t stop until we get that.”
The police might not always find the answers, but they won’t stop either.
Full list of unsolved murder cases:
George (64) and Lillian (67) Peach. Murdered in their home. Ashton, near Oundle. 1952.
Avis West (82). Murdered in her home. Northampton. 1976.
Sean McGann (15). Strangled and body left in alleyway. Northampton. 1981.
Susan Ovens (27), Sidney Hickling (27) and Dolphus Smith (57). Shot at close range in their caravans. Rushden. 1981.
Unidentified baby (age unknown). Found in lane strangled by cloth. Northampton. 1982.
Cyril Fensome (62), Florence Pennell (60) and Stacey Darlington (7). Petrol poured in letterbox and set alight. Northampton. 1987.
Carol Baldwin (13). Stabbed in the chest in a park. Northampton. 1988.
Percy Francis (70). Stabbed and hit with object. Rushden. 1988.
John Reynolds (40). Shot whilst walking dogs. Rushden. 1993.
Arthur Brumhill (76). Found dead in shop basement. Northampton. 1993.
Albert Bowers (57). Beaten and later died of blood clot. Northampton. 1998.
Mithat Lleshi (23) and Astrit Cakoni (28). Attacked outside shop. Northampton. 2001.
Sarah Benford (14). Missing person last seen in 200. Kettering. Murder enquiry since 2003.
Callum Bland (3). Died in arson attack on his house. Wellingborough. 2007.
Mavis Clift (65). Died after house set on fire. Northampton 2008.
Abdi Leban (32). Died in suspicious fire in block of flats. Northampton. 2008.
Karoly Varga (76). Found dead at home with head injuries. Wellingborough. 2011.
David Ross (39). Found dead in hotel room. Corby. 2012.
Jon Casey (35). Stabbed outside restaurant. Northampton. 2015.
Helen Gormeley (64). Missing person since 1986. Case taken over by Humberside Police. Murder enquiry since 2015.
Adeyemi Olugbuyi (32). Remains found by litter picker. Northampton. 2015.
David Brickwood (74). Violent assault at home during burglary. 2015.