Crime scene forensics: How does it work?

CSI: NY, Gary Sinise, 'Smooth Criminal' Shows like CSI tend to simplify police forensics

The conviction of two men for the murder of Stephen Lawrence has cast the spotlight on the painstaking work involved in forensic science. After months, or even years, of police work a case often ends up in a courtroom but where does the science fit in and what has to be proved?

From CSI and countless TV police procedurals, ordinary people think they are familiar with the world of forensic science.

But while most trials now have an element of forensic science - whether it is fingerprints, DNA, blood or fibre analysis, mobile phone "cellsite" data or ballistics evidence - it is not always as clear-cut as it is on TV.

Detectives must painstakingly gather it and back it up with other evidence, then prosecutors must make it clear and comprehensible to a jury.

Fingerprints

Jonathan Palmer Jonathan Palmer staged the crime scene to suggest his wife had been killed by burglars

Fingerprints have been a key part of the police's toolbox for more than 100 years. Now they can be scanned onto a laptop by a crime scene officer to look for matches with convicted criminals and suspects within minutes.

If there is no match, investigators might get prints from family, friends and neighbours.

"You have no right to force them to give their fingerprints but they would attract a higher level of interest if they refused," says retired Detective Chief Superintendent Martin Bottomley, of Greater Manchester Police, who works as a civilian on the force's cold case team.

"Once you have identified the owner of the prints you will look at the background to see whether he or she could have an innocent explanation or whether there is something dark or nefarious about their presence."

Bloody fingerprints are almost guaranteed to lead to a conviction, unless the defence lawyer can persuade a jury his client became bloodied when he discovered the crime scene.

In that case, it requires a skilled line of questioning from the prosecuting barrister to tease out inconsistencies in the defendant's story.

Three days before Christmas 2009, Melinda Palmer, 57, was bludgeoned to death at her home in Worcestershire.

Case of the bloody palmprint

  • June 2008: Two French students tortured and murdered in their flat in south London
  • April 2009: Dano Sonnex and Nigel Farmer go on trial. Confronted by his bloody palmprint at the scene, Sonnex admits burglary but denies murder.
  • May 2009: Sonnex is cross examined by Crispin Aylett QC and shows flashes of his psychotic temper
  • June 2009: Both are jailed for life for murder. Sonnex is locked up for minimum of 40 years

A bloody fingerprint belonging to her husband, Jonathan, was found on a door.

Forensic evidence suggested the body had been moved from where she was attacked and clues suggested her bleeding head had been wrapped in clingfilm at one point. Both suggested Palmer had staged the crime scene to point towards burglars.

In summer 2010, Palmer went on trial. Stephen Linehan, the Birmingham-based QC who prosecuted him, explains how Palmer claimed in court he must have left the print after he found the body and shut the door.

But Linehan says: "The position of the print did not fit with where your hand would be if you shut the door. It was an important point and one which the jury had to understand."

In September 2010, Palmer was jailed for life.

DNA

The conviction in 1987 of Colin Pitchfork - jailed for life for murdering two teenage girls near Leicester - was the first time DNA had been used to catch a killer.

Evidence against Khalid Sarwar DNA on the glove (bottom left) was part of the evidence which convicted Khalid Sarwar

Since then thousands of murderers, rapists and robbers have been locked up thanks to DNA. Many are "cold cases", where the files of unsolved crimes have been dusted off and detectives scour old clothes and other exhibits in the hope of finding a DNA profile.

Such a case is the rape and murder of 17-year-old Dorothy Leyden in Manchester in 1971, which featured in the BBC's Crimewatch programme.

"We found old exhibits from the case in the basement of a police station and from a blackened piece of cotton wool in a test tube we managed to extract a full DNA profile of the attacker," says Bottomley.

DNA evidence, backed up by strong circumstantial evidence, can be decisive.

Khalid Sarwar went on trial in 2010 for murdering Glasgow radio agony aunt Nasim Jamil.

During the trial the jury was told DNA was found on a glove near the dead woman and the chances of it matching someone unrelated to Sarwar were one in a billion.

The Lesley Molseed case

  • Oct 1975: Lesley Molseed, 11, murdered in Rochdale
  • 1976: Stefan Kiszko convicted of murder but later cleared after 16 years in jail
  • 2005: Case reopened after DNA profile found on Lesley's underwear
  • Nov 2006: Ronald Castree charged with murder after his DNA matched profile
  • Nov 2007: Castree jailed for life

Sarwar's lawyer, Donald Findlay QC, one of Scotland's top barristers, said finding DNA on an object did not show how it had got there or when, and forensic scientist Carol Weston had to agree.

But Sarwar, who had also dropped a bloodstained note, in his handwriting, at the scene, was convicted of her murder and jailed for life.

In recent years, DNA has also helped to clear several people who were wrongly convicted. One of the best known cases was Sean Hodgson, who spent 27 years in prison for the murder of a woman in Southampton.

A new inquiry in 2008 revealed David Lace, who died in 1988, was the actual killer.

Blood and fibre analysis

The discovery of blood, fibres or body hairs can be quite incriminating but it often takes skilled detective work to get a conviction.

Bottomley cites the case of 15-year-old Mandy Hardwick, who was strangled and dumped in a street in the Collyhurst district of Manchester in 2004. Tiny traces of hair were found on the body and Michael Hardy was identified as a suspect by experienced detectives.

The case of the bloody flat

Derek Brown
  • Derek Brown was charged with the murder of two women whose bodies were never found
  • In court Brown claimed two "mean-looking" Chinese men had beaten Xiao Mei Guo in his flat, bloodying her nose
  • He also claimed he left prostitute Bonnie Barrett in his flat with two bikers who he had met in a pub
  • Confronted with forensic evidence he refused to answer any more of prosecutor Brian Altman's questions in the witness box
  • In October 2008 Brown was jailed for life and ordered to serve a minimum of 30 years

Bottomley, who works for Greater Manchester Police's Major Crime and Cold Review team, explains: "During careful questioning he declared that he had cut his hair with a razor around the time she went missing.

"That tiny lead, obtained by good old detective work, led to him being identified as a suspect.

"Her body was found fully clothed but forensic tests were carried out on her body and it became clear that she was covered in tiny pieces of hair, which linked his presence to her naked body."

Hardy was interviewed 23 times and it was only on the 23rd time, with the account of the scientific evidence, that he admitted what had happened, says Bottomley.

"He said 'the scientists are right' and then he admitted to strangling and dumping her." In April 2005 he was jailed for life for the teenager's murder.

There could always be an innocent explanation for blood at a crime scene or on a defendant's clothes. Analysis of the blood - and the presentation of that in court - is key.

In the case of Derek Brown, jailed for life in 2008 for murdering two women whose bodies were never found, there was blood all over his flat. Brown came up with a preposterous story to explain the presence of the women's blood.

But he was so flummoxed by the evidence against him and his cross examination by Brian Altman QC -one of the country's top prosecutors and First Senior Treasury Counsel - that he refused to answer any more questions, effectively throwing in the towel.

"The jury convicted him in two hours so again the scientific evidence [was] absolutely critical," says Altman.

Ballistics

Tackling gun crime is a fact of life for detectives in many urban areas - London, Manchester, Birmingham and to a lesser degree Glasgow, Leeds and Nottingham. Ballistics is at the heart of these investigations.

A gun used in the murder of PC Patrick Dunne Every gun has its own distinct ballistics footprint

If shell casings are recovered but not the gun, they will be sent off for examination and checked against the Nabis (National Ballistics Intelligence Service) database, says Bottomley.

"It will say if the gun was used 18 months ago in a shooting in Longsight [Manchester] or last week in the West Midlands. Guns do travel around the country like that."

Whatever a ballistics examination tells the detective, more work is necessary. If a suspect emerges their home might be searched and with luck police might discover a gun or traces of firearms residue.

But Bottomley explains: "Firearms residue is not like DNA. Residue from a Beretta is not dissimilar to a Luger."

And with few people in Britain having first-hand knowledge of guns, the likelihood is that a jury will need to be carefully led through ballistics evidence by a prosecutor.

Brian Altman's casebook

  • 2007: Stuart Harling convicted of murdering nurse Cheryl Moss as she took a cigarette break. Harling feigned mental illness at trial.
  • 2008: Mark Dixie convicted of raping and murdering Sally Anne Bowman. Dixie claimed in court he had sex after finding Sally Anne's body
  • 2009: Samantha Joseph and six others convicted of "honey trap" killing of teenager Shakilus Townsend
  • 2010: Two people convicted of homophobic killing of Ian Baynham in Trafalgar Square. There was compelling CCTV evidence
  • 2011: Levi Bellfield convicted of murdering schoolgirl Milly Dowler. Bellfield had earlier been found guilty of two other murders

The terminology involved, as explained in this BBC glossary, takes some explaining but the science of ballistics can be used to determine from what angle and distance a gun has been fired, as well as to link weapons to shootings.

Brendan Morris, who has prosecuted many gun trials, says: "It can be quite hard to link a gun to a suspect. It may involve fingerprints, DNA and weapons discharge. Whenever a gun is fired various metals and gases are discharged and they stick to skin or material.

"Sometimes the defence can claim there has been contamination, for example if a suspect has been arrested by firearms officers or has sat in a police car where guns have been."

Mobile phones

Many criminals are aware of how easy it is for police to establish their location at or near a crime scene using mobile phone evidence.

'Happy slapping' murder

  • Oct 2004 - Gay barman David Morley beaten to death by a gang on London's South Bank
  • Nov 2005 - Four people go on trial. An Old Bailey jury is told one of the defendants stole Morley's phone during the "happy slapping" attack and later phoned his own girlfriend on it. Chelsea O'Mahoney, 16, filmed the attack on her mobile phone
  • Dec 2005 - Four people, aged 16 to 21, jailed for manslaughter.

"Sophisticated career criminals, contract killers and robbers will use the pre-paid non-subscriber mobile phones and dispose of them regularly, or after a crime," says Bottomley.

"But most murders are committed on the spur of the moment, whether it be a crime of passion or a fight in a pub or even a gang crime and in that case they won't have been so careful with their phones."

Suspects often claim they had lent their phone to a friend or had it stolen. Sometimes detectives may be able to prove, from mobile phone records, that a suspect has lied about not having the phone with him, for example if they can find a call he has made to a close relative or a girlfriend.

But Bottomley says: "The fact that you can prove someone is a liar is not enough to prove they are a rapist or murderer. You have to have tangible evidence."

Mobile phone evidence - known as cellsite analysis - was first used in trials in the late 1990s and was often baffling and poorly prepared.

Now Powerpoint presentations and colour coding are used - to use a fictional example, Freddie, the hitman, used the blue phone from the crime scene, seconds after a murder to call Billy, the victim's husband, on his yellow phone.

"So the jury can see very readily where individual A was at a particular time when a particular text or call was made and so what we are seeking to do is to make the presentation of highly technical evidence user-friendly," says Altman.

Charlene Ellis (second left) and Letisha Shakespeare (far right) Charlene Ellis (second left) and Letisha Shakespeare (far right) were gunned down in 2003

A classic example was the trial in 2005 of four members of the Burger Bar Boys gang for murdering two girls in Birmingham two years earlier.

The jury was shown a Powerpoint presentation which showed a mobile phone belonging to one of the defendants, Nathan Martin, travelling from Birmingham to Northampton and back.

When it was matched with evidence from Automatic Number Plate Recognition cameras on the M6 and M1 it proved Martin was buying the getaway car used in the murders, which was picked up in Northampton two days before.

CCTV cameras

The number of CCTV cameras in Britain has risen massively over the last decade.

In December 2010, Detective Chief Inspector Mick Neville, of Scotland Yard's identification unit, said 2,512 suspects had been caught through CCTV in the last 12 months, including four suspected murderers, 23 alleged rapists and sex attackers and five gunmen.

But the idea that the images are usually high quality or can be easily enhanced is wrong.

"You have to work with what you've got and if the original image is low resolution then no amount of enhancing will really improve it," says Bottomley.

Caught on camera

Ruby Thomas and Rachel Burke
  • One night in September 2009 Ian Baynham was attacked in Trafalgar Square
  • Police later put out this CCTV image of two teenage girls seen nearby
  • The girls were later identified as Ruby Thomas and her friend Rachel Burke
  • Thomas was later convicted of manslaughter and Burke was guilty of affray
  • Thomas was jailed for seven years, Burke for two

But detectives do use facial imaging and body language experts to determine if an individual on camera matches their suspect.

"They can compare the length of the nose or the forehead or can look at logos on shirts or whether the person sticks their left elbow out as they walk," he explains.

Altman used CCTV evidence recently to obtain the conviction of the homophobic killers of Ian Baynham in London's Trafalgar Square.

Ruby Thomas, 18, and Joel Alexander, 20, were both found guilty of manslaughter.

In a courtroom, a prosecutor must not only prove there is no mistaken identity - some defendants will deny it is them even though the footage is obvious - but also that they did not have an innocent reason for being at the scene.

CCTV footage of nightclub scenes or street melees can often be confusing and care has to be taken to identify the guilty by their clothes, height, haircuts and any other distinguishing marks.

"If there was political will to it and resources, which aren't overflowing at the moment, standardisation of top quality CCTV in town centres and elsewhere would make a huge difference to what we do," Altman suggests.

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