Bloodstain Removal - a Killer's Dilemma

‘Did you ever notice how they have commercials on TV with detergents that can get out bloodstains?  If you have blood all over your shirt, I don’t think laundry is your biggest problem’.  Jerry Seinfeld  

It is virtually impossible to remove bloodstains from a crime scene.  The assailant who has killed his victim in a kitchen or bathroom with easy to clean surfaces may feel confident that no trace of his crime remains.  However, tiny specks of blood can remain in the room and, crucially, may still be there many years after the killing. 

A particularly difficult cleaning problem confronts the assailant who has committed his murder surrounded by absorbent surfaces like carpets, curtains and bedding.  Cold water is probably the most effective way to remove bloodstains – to the naked eye, at least.  Hot water just fixes the stain and the use of chlorine-based bleach turns the bloodstain a pale green-brown.

Blood visualisation chemicals, such as the highly sensitive Bluestar®  Forensic reagent, can reveal the presence of bloodstains that have been wiped away, washed out, or are invisible to the naked eye.  The haemoglobin (an oxygen-carrying protein) in the blood reacts with the chemicals in the reagent to produce the glow-in-the-dark effect much beloved of television producers.  This process is known as chemiluminescence. 

But what if a substance existed that would remove haemoglobin? Bluestar® Forensic reagent cannot work without the presence of haemoglobin. 

I mentioned that chlorine–based bleach is ineffective at bloodstain removal.  However, there is another type of bleach found in some household cleaning products – including washing powder – that contain oxygen bleach.  Scientists at the University of Valencia in Spain have discovered that oxygen bleach removes haemoglobin.

Their tests showed that washing powders containing oxygen bleach will not only make bloodstains fade but they will also make them unreactive to blood visualisation chemicals, owing to the removal of the haemoglobin from the stain.

The killer’s dilemma now becomes the forensic scientist’s dilemma. Even if a stain is still visible, because it is unreactive, it will not automatically be tested for DNA, since it has not been verified as being of human origin.  This means that useful evidence may, potentially, be lost.

But, it takes only a drop of the victim’s blood on a suspect’s clothes to confirm that the suspect was at the scene at the time of the attack.  Blood embedded in the seams is very resistant to washing and can be easily missed in the assailant’s clean-up operation.