The search for missing RAF airman Corrie McKeague is the most expensive investigation Suffolk police has carried out in the last 10 years, it has been revealed.

According to a Freedom of Information request, the amount of money spent on the probe is just £30,000 shy of the cost of all nine other operations combined - which include the murder of Tavis Spencer-Aitkens, and the double murder of Peter and Sylvia Stuart in Weybread.

Corrie, who was based at RAF Honington, vanished without a trace in September 2016.

Police spent several months searching a landfill site in Milton, Cambridgeshire, because they suspected the 24-year-old may have fallen asleep in a bin.

Explaining why the cost of investigations can differ, police said: "Major investigations are often very complex and by their nature are likely to be long-running, which means the costs can vary and resources may fluctuate.

"Each investigation is unique and we will continue to investigate thoroughly and appropriately in order to bring as many as we can to a conclusion."

Private detectives were not used in any of the below operations, they added.

The top 10 most expensive police operations in Suffolk since 2009

*Figures exclude officer salaries and are correct as of March 2019

1. Operation Phonetic - Missing person Corrie McKeague, 2016

East Anglian Daily Times: Corrie McKeague search starts at the Milton Landfill site in Cambridgeshire. Pictures: GREGG BROWNCorrie McKeague search starts at the Milton Landfill site in Cambridgeshire. Pictures: GREGG BROWN

Money spent: £1,344,535

In January 2018 it was revealed the total cost of the hunt to find Corrie, who disappeared after a night out in Bury St Edmunds on September 24, 2016, had topped £2.1million, with £826,000 of that figure used to fund officer salaries.

Without police staff costs and costs incurred to backfill officers drafted in for the search, Suffolk Constabulary said £1.34million has been spent on the investigation to date.

Police say the investigation costs have been calculated by reviewing overtime expenditure allocated to Operation Phonetic, landfill search costs and a calculation of normal officer salary payments, based on the number of police officer hours allocated to the investigation.

In December 2017, Suffolk's police and crime commissioner Tim Passmore asked the government to pay for the £1.5m landfill search.

East Anglian Daily Times: Nicola Urquhart, the mother of missing Corrie McKeague, returns to Bury St Edmunds where her son was last seen Picture: Neil DidsburyNicola Urquhart, the mother of missing Corrie McKeague, returns to Bury St Edmunds where her son was last seen Picture: Neil Didsbury (Image: Archant)

MORE: Corrie McKeague's mum 'ready to start searching again'

2. Operation Cannington - Gun haul at Wyverstone, 2014

Money spent: £267,780

Police found more than 400 firearms at the home of parish council chairman James Arnold in Wyverstone, Suffolk, in April 2014.

It was the largest ever stash of illegal weapons seen in the UK.

East Anglian Daily Times: James Arnold, who died of cancer before he could face trial Picture: SUFFOLK CONSTABULARYJames Arnold, who died of cancer before he could face trial Picture: SUFFOLK CONSTABULARY

There were 463 firearms discovered - 177 of them were rifles, 136 were handguns, 88 were shotguns and 38 were machine guns.

Officers on the case found the weapons in a secret room in Arnold's house.

The room was accessed through a hidden door in his kitchen.

Officers also found a safe behind a false wall.

Arnold died of pancreatic cancer three months after the discovery, but arms dealer Anthony Buckland was jailed in February 2016 for supplying some of the weapons to him.

East Anglian Daily Times: The extension James Arnold put on the side of his house which he used as a hide Picture: SUFFOLK CONSTABULARYThe extension James Arnold put on the side of his house which he used as a hide Picture: SUFFOLK CONSTABULARY (Image: Archant)

MORE: Photos show UK's biggest haul of weapons found in Suffolk

3. Operation Chertsey - Murder of Dean Stansby, 2017

Money spent: £228,876

Father-of-five Dean Stansby, from Trimley, was stabbed in Ipswich's Ancaster Road on February 8, 2017.

He was found collapsed by a member of the public and rushed to hospital, but he died of a stab wound to his stomach.

East Anglian Daily Times: Father-of-five Dean Stansby was stabbed near Ipswich railway station Picture: CONTRIBUTEDFather-of-five Dean Stansby was stabbed near Ipswich railway station Picture: CONTRIBUTED (Image: Archant)

Police launched a murder inquiry and a series of arrests were made in connection with the attack in the week that followed.

Posters were put up around Ipswich asking for the public's help with the investigation.

CCTV footage from the night in question was scoured by officers and countless witness statements were taken in connection with the incident.

The following year, four people were jailed for life for murdering Mr Stansby.

MORE: Brother's knife crime plea follows guilty verdicts for Dean Stansby's killers4. Operation Ruddock - Murder of Tavis Spencer-Aitkens, 2018

East Anglian Daily Times: Tavis Spencer-Aitkens Picture: SUPPLIED BY FAMILYTavis Spencer-Aitkens Picture: SUPPLIED BY FAMILY (Image: Archant)

Money spent: £189,970

Ipswich teenager Tavis Spencer-Aitkens was stabbed to death in Packard Avenue on June 6, 2018.

In the days after the killing, mobile police stations were set up to reassure the community.

During a four-month murder trial, the court heard the attack on Tavis was the result of what the JBlock gang from the Jubilee Park area of Ipswich perceived to be a loss of respect following a row between two of their friends, and two of Tavis' friends, earlier on the day of the killing.

Following the attack on Tavis in Packard Avenue, his step-sister rushed to his aid and saw a deep cut to his throat and a number of injuries to his back.

East Anglian Daily Times: Five people were found guilty for killing Tavis Spencer-Aitkens Picture: SUFFOLK CONSTABULARYFive people were found guilty for killing Tavis Spencer-Aitkens Picture: SUFFOLK CONSTABULARY

In April this year, his killers were jailed for more than 100 years.WATCH: Film explores what led to the rise of youth violence in Ipswich5. Operation Sunlight - Double murder of Nathan Oakley and Barry Street, 2016

Money spent: £188,601

Travellers Barry Street, 32, and Nathan Oakley, 18, were both stabbed at the West Meadows site in Ipswich on December 8, 2016.

Police rushed to the scene of the attacks, but both men died within an hour.

Helicopters, dog units and ambulances were all dispatched and a teenager was arrested in connection with the stabbings a few days later.

East Anglian Daily Times: Murder victim Barry Street, pictured here after he was jailed in 2004, was stabbed at the West Meadows travellers site in 2016 Picture: SUFFOLK CONSTABULARYMurder victim Barry Street, pictured here after he was jailed in 2004, was stabbed at the West Meadows travellers site in 2016 Picture: SUFFOLK CONSTABULARY

Nelson Smith was later convicted of murdering father-of-three Mr Street and the manslaughter of Mr Oakley.

The 18-year-old stabbed the pair during a "chaotic brawl" at the West Meadows site in Bury Road following a row over a Red Bull can, Ipswich Crown Court heard.

Smith claimed he grabbed a knife and stabbed the two men repeatedly from behind to stop them viciously beating his father Nelson Smith Senior.

6. Operation Seminar - Double murder of Peter and Sylvia Stuart, 2016

Money spent: £163,211

East Anglian Daily Times: Peter and Sylvia Stuart, from Weybread Picture: SUFFOLK CONSTABULARYPeter and Sylvia Stuart, from Weybread Picture: SUFFOLK CONSTABULARY (Image: Archant)

Retired couple Peter and Sylvia Stuart, who lived in Weybread, near Diss, vanished from their home in June 2016.

The body of Peter, 75, who had been stabbed nine times, was found in a ditch in woodland close to his home in Mill Lane.

His wife Sylvia, 69, has never been found.

Ali Qazimaj, 45, of Tilbury, Essex, was jailed for a minimum of 25 years in 2017 after being found guilty of the murders.

Andy Guy, a former Detective Chief Inspector with Norfolk police, told a national documentary about the killings he was "absolutely convinced" there was "absolutely no way" that Mrs Stuart was still alive.

East Anglian Daily Times: Al Qazimaj was found guilty of murdering Peter and Sylvia Stuart Picture: NICK BUTCHERAl Qazimaj was found guilty of murdering Peter and Sylvia Stuart Picture: NICK BUTCHER (Image: �archant2016)

Now the force's unsolved case review manager, Mr Guy said around 950 proof of life enquiries were carried out and large-scale searches carried out but nothing was found to suggest she was still alive.

MORE: Documentary featuring double Suffolk murder airs on national TV 7. Operation Calne - Murder of Peter Avis, 2012

Money spent: £120,052

Jeweller Peter Avis was found dead at his flat above Collis & Son in Abbeygate Street, Bury St Edmunds, on January 13, 2012.

The 66-year-old, who lived alone and had difficulty walking, had been stabbed 13 times and had been hit in the face with a glass ashtray.

East Anglian Daily Times: Jeweller Peter Avis, 66, was killed in a burglary gone wrong Picture: SUFFOLK CONSTABULARYJeweller Peter Avis, 66, was killed in a burglary gone wrong Picture: SUFFOLK CONSTABULARY (Image: Archant)

He was found lying on his bed in papers which had been thrown from drawers as the property was ransacked in a "botched" burglary.

Police managed to recovery jewellery and silverware with an insurance value of more than £17,000, but a murder trial heard it was not clear exactly what had been stolen during the raid.

Ireneusz Melanuik was jailed for 25 years for murdering Mr Avis, while four others were sentenced for burglary offences.

8. Unknown operation

Money spent: £82,321

East Anglian Daily Times: Suffolk police were unable to specify which operation they spent �82,321 on Picture: STOCK PHOTOSuffolk police were unable to specify which operation they spent �82,321 on Picture: STOCK PHOTO (Image: Archant)

This particular operation was categorised as 'sensitive' and could not be disclosed to this newspaper under the Freedom of Information Act.

Giving details of this investigation was considered by Suffolk Constabulary to be detrimental to its abilities to effectively enforce the law, prevent and detect crime, and protect local communities.

9. Operation Kruse - Murder of Mary Roberts, 2013

Money spent: £71,323

Vulnerable Mary Roberts was found collapsed in a car park at the back of a pub in Bury St Edmunds in on March 27, 2013.

East Anglian Daily Times: Mary Roberts, 50, was strangled in Bury St Edmunds Picture: SUFFOLK CONSTABULARYMary Roberts, 50, was strangled in Bury St Edmunds Picture: SUFFOLK CONSTABULARY

The 50-year-old was pronounced dead at the scene and a murder enquiry was launched.

Later that afternoon, officers arrested Mary's flatmate Andrew Ratcliffe on suspicion of murder.

Police sifted through several hours of CCTV footage in preparation for a murder trial, where Ratcliffe was found guilty and sentenced to life in prison.

Ipswich Crown Court heard Mary had been strangled and sexually assaulted.

10. Operation Wakerley - Murder/suicide of Fiona Anderson and her three children, 2013

East Anglian Daily Times: Fiona Anderson, who was found dead in Lowestoft. Her three children were found dead later that day Picture: SUFFOLK CONSTABULARYFiona Anderson, who was found dead in Lowestoft. Her three children were found dead later that day Picture: SUFFOLK CONSTABULARY (Image: Suffolk Constabulary)

Money spent: £63,634

Fiona Anderson was found dead after falling from a building in Lowestoft on April 15, 2013.

A few hours later and her three children were also found dead at their home.

Three days later, the senior detective leading the investigation confirmed police were not looking for anyone else in connection with the "tragic deaths".

An inquest into their deaths found Miss Anderson took her own life, and that the three children were unlawfully killed.

MORE: Fiona Anderson case - A timeline of tragedy