Time of death

 

Martin Grassberger is a forensic pathologist at the Medical University of Vienna with an interest in the entomology of crime scenes.  He studies insect development and populations on corpses as a guide to calculating how long the body has been dead.  He doesn’t use human corpses in his work (this is considered unethical), but employs clothed pig standins.  An early episode of CSI had a forensic detective doing just that, but there the resemblance to reality stopped. ‘They had the detective measuring adult insects and consulting a table that told him how long the body had been dead, and bingo, case solved,’ says Martin. The producers had clearly decided that showing maggots at different stages of the insect life cycle was too disturbing for viewers.  In reality adult insects don’t grow, it’s the larval forms that grow so the length of adult insects can tell you nothing about the time since death.  Real science was mixed with total fiction yet again.  

 

How many times have you seen the pathologist casually glance at the murdered body and announce to the waiting police detective that the body has been dead for two to three hours.  

It is actually very involved and difficult to establish time of death.  Bodies cool at a fairly predictable rate given that you know the surrounding temperature, whether the body is fat or thin, exposed to the weather etc but even making this test using internal temperature can only give a accuracy of 5 – 6 hours, say the murder happening between 3 and 9 in the morning.  To narrow the result further, the pathologist has to look at the state of rigor mortis of the body (stiffening after death), test the iris using drugs, and examine the electrical response of facial muscles.  Even all this will only narrow time of death a little further.  The frequent TV test of how much the last meal is digested is almost never used because it is so inaccurate.  After 24 hours the only reliable tests are based on insect colonisation.

 

Copycat criminals

 

Police officers and judges watch these shows and often expect the expert witness to use the same techniques and draw the same conclusions as the television actors.   ‘What’s worse, real life criminals also watch and have started to wear latex gloves and avoid leaving evidence like cigarette butts behind at the scene,’ says Martin, criminals are becoming more sophisticated from their TV education in forensics, and while it is certainly true that technology and science are becoming ever more important tools in crime solving, the human contribution of the skilled forensic specialist will always be critical.

 

 

 

 BOXOUT DNA Profiling

 

The UK has the world’s largest database of DNA profiles, holding almost 3 million samples and has matched nearly 600,000 suspects to crimes.  Each month police match crime scene samples with profiles from the database to come up with a suspect in 15 murders, 45 sexual offences and 2500 vehicle, property and drug crimes.  With DNA evidence, police clear up rates in the UK go up from 24 per cent to 43 per cent.  98 % of profiles are from men.

 

DNA can be retrieved from blood, semen, saliva, skin or hair left behind at the scene of a crime or voluntarily provided to clear a potential suspect.  Large portions of every human being’s DNA are the same as anyone else’s (it is what makes us human after all), but DNA profiling focuses on 10 markers or extremely variable parts of our DNA that together are unique to the individual. Only identical twins have the same DNA.  Besides proving guilt, a non matching DNA profile can exclude the innocent.  In the USA, people on death row have been freed based on DNA evidence and about 30% of profiles done by the FBI result in people being eliminated as suspects.  DNA profiling is also used to pinpoint whether or not someone is the father of a child.  

 

DNA testing is getting faster but not as fast as the TV shows would have you believe.  One of the fastest tests on record was when Saddam Hussein was arrested in 2003.  The former dictator of Iraq had so many body doubles that authorities needed to confirm his identity from his DNA.  The test took seventeen hours to come up with a result.  More normally in routine police work the test take two to three weeks.