Part 7: How is it done?

This murder case is getting to be more and more interesting. As of now, the doctors have developed a DNA profile and it showed clear evidence for a father and son. Also, they got lucky! There was another DNA profiling pattern that matched a living twin; Tanya Rosilawati. With this, now we are to match the evidence to these victims who were earlier filed for missing person, namely Herman Hartono, Adi Hartono and Anya Suriati. Now, we are one step away from solving this gruesome murder! 

Now, to reaffirm the identity of the victims with the people from the missing people list, we have to compare ante mortem records with that of the postmortem.

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POSTMORTEM RECORDS

We shall start off with the methods of obtaining the post mortem results:

First off, we have to extract the DNA from the evidences that were found previously, which were:

-   Skull and jaw of an adult bearing five teeth

-   Fragments of a jaw with three molars

-   Jaw of a child with teeth still erupting

Unlike nuclear DNA,  mitochondrial DNA is present at levels of more than 103 or 104 copies/cell and can be amplified from highly degraded samples using the polymerase chain reaction (PCR) technique, which will be elaborated further on. Once we have already grasp this concept, we now have to extract the mitochondrial DNA from the tooth dentine. "Why the tooth dentine?" you may ask. 

Why the tooth?

Well, since dentine and pulp is covered with enamel (the outer layer as well as the hardest part of tooth) both are resistant to incompatible conditions for DNA. Therefore, in extreme conditions such as when the condition of the body which has been decomposed or burnt, dentine remains as a better source of DNA, particularly mitochondrial DNA.

Mitochondria!

             

Once the DNA samples have been obtained, it will be analysed and the analysis of the DNA is known as DNA Profiling or DNA typing. 

What is DNA?

DNA is found in the cells of all living things, including the human body.

A person will have the same DNA throughout their body in every cell with a nucleus. That is, the same DNA profiling results for one person will be obtained whether testing blood or semen or muscle tissue.

Cool animation... DNA!

Basically, the DNA molecule:

- consists of two strands twisted about each other in the shape of a spiral staircase 

- has 4 different types of bases

- each type of base will only bind with another specific type

- the two strands are 'complementary'

For what cases is DNA profiling used?

Usually, DNA profiling is carried out when human biological fluid or tissue is found at a crime scene and used as evidence to solve the crime such as in this case. For example:

• A murder where it appeared that a struggle took place and blood from the murderer was left at the scene. This would be compared to a sample of blood from the suspect.
• A murder where a blunt instrument was used and a suspect was found with a club on which there were dried blood stains. The blood on the club would be compared to the victim's blood.

DNA molecule

DNA profiling can only be used if there is enough DNA in the samples. Crime samples can be compared to a sample from a known suspect or compared to a database of DNA profiling results from other scenes or from convicted offenders. If there is a 'match', the two samples may have originated from the same person.

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There are two DNA profiling techniques used in forensic science laboratories throughout the world;

1.     Restriction Fragment Length Polymorphism (RFLP);

2.     Polymerase Chain Reaction (PCR)

    

It involves cutting up the DNA into small fragments with molecular scissors known as restriction enzymes and determining their length. This is done by electrophoresis, that is placing the fragments on a gel that acts as a molecular sieve. When a voltage is applied the larger fragments travel a lesser distance than the smaller ones because the gel molecules hinder the movement of the fragments.

The DNA fragments on the gel are then transferred to a special membrane to which is applied a 'probe', a radioactive piece of DNA that specifically attaches to certain fragments depending on their type .The position of the probe is found by placing the membrane next to a sheet of radioactive film, resulting in the DNA fragments appearing as 'bands'.

How PCR is done.

Detecting the variation

A detection system is required to determine the difference between DNA types once amplification has taken place. The detection system used depends on the type of variation, that is either the sequence or length.

Using this method, the variation is detected using electrophoresis. The millions of copies of DNA produced by the PCR reaction are placed on a gel in a line. An electrical voltage is applied to the gel and the DNA then travels through the gel because of electrical charge of the DNA molecules. The larger molecules travel a shorter distance through the gel than the smaller ones because the gel molecules hinder the movement of the DNA. The distance the DNA copies have traveled through the gel is compared to the distance that known standards have traveled.

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What do the DNA profiling results mean for a case?

DNA profiling does not claim to be absolute identification, but may be very strong evidence, and generally forms just one part of a case. It is really a question of looking at all the evidence in the case such as; who had the opportunity to commit the crime, eye-witness descriptions, fingerprints, the transfer of glass fragments, paint flakes or fibres linking a person to a crime and the DNA profiling results. DNA profiling is presented to the court as in the example above and the jury or magistrate can draw their own conclusions, as they do about all the evidence.

DNA profiling can be a very powerful investigative tool. Of the cases carried out so far, approximately fifty percent of the profiling results have established that the suspect was not the source of the sample associated with the crime - i.e. he/she was excluded as being the perpetrator of the crime.

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ANTEMORTEM RECORDS

Okay, after knowing the methods and gathering postmortem  records we need ante mortem records for comparison. Various methods of records are available for comparison;

1) X-rays

They are one of the most important antemortem records.These x-rays may reveal additional information and may compare more favorably with the postmortem x-rays of the remains.Also it is important to obtain the most recent ante mortem records as most individuals have probably been treated by more than one dentist throughout their lifetime.

X-ray showing a person's teeth.

What if they have no dental x-rays? Not to worry!

If conventional dental x-rays are unavailable, we can recover medical or chiropractic x-rays that may show the teeth.

2) Study models or casts of teeth 

Cast of teeth

These are also very useful in comparison with postmortem evidences. They can usually be obtained if patient has history of orthodontic treatment.

3) Photographs

Various sources can be searched. They can be acquired from dentist documenting their patients dental condition or simply family snapshots or any picture from gatherings wedding or graduation with the person smiling.These can help as teeth may be visible showing missing teeth, discoloration, any breaks or any chip in the tooth. These visual evidences are distinct and can aid in identification with comparison with postmortem evidences.

                                                                       

THE END.