Identical twins have always fascinated us. We can’t help but be intrigued by two people who look the same, act the same, dress the same. There are tales of cute little girls with matching ribbons and boisterous boys with identical crew cuts, but there are also tales of violent crimes remaining unprosecuted because police are unable to determine which twin carried out the crime in question.

Eyewitnesses can give a description of the individual they saw, but when presented with two identical versions of that individual, they are at a loss to distinguish between them. Tattoos, scars or injuries can be a method of telling twins apart but when such visual marks are not an option; a case can become reliant on forensic evidence. Forensic evidence that for identical twins, can be a complex web to navigate.

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Monozygotic twins are identical because they come from the same egg inside the womb splitting in half and as a result, they also have identical DNA sequences when their genetic profiles are examined using standard forensic testing techniques. This means that while a DNA sample may be found at a crime scene, if this DNA is matched to a pair of identical twins it is impossible to know which twin it came from. From a legal standpoint, this leaves prosecutors with few options in a court of law when the forensic evidence cannot identify the individual responsible for the crime.  Rather than risk charging and potentially convicting the wrong twin, many criminal cases have been dropped as a result.

The Cooper twins in Grand Rapids in Michigan are one example. After a female was attacked and raped in November 1999 forensic investigators obtained a DNA profile of her attacker which matched the DNA samples of Tyrone and Jerome Cooper. Both men had histories of sexual assaults against women reports CNN and when questioned both categorically denied carrying out this offence. This case remains officially unsolved as a result with prosecutors unable to bring charges without knowing which twin they should be charging.

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Tyrone and Jerome Cooper

A further problem which has been encountered in criminal cases involving twins is where one twin is accused of harming the other. When forensic evidence is collected at a crime scene the DNA of the victim will, of course, be present and what investigators are looking for is a second DNA profile to identify the offender. In the case of identical twins that have identical DNA, this method of crime scene analysis becomes unusable.

In September 2011, Wael Ali was arrested and charged with the murder of his twin brother who was found dead in woodland in Columbia, Maryland in August 2007. Wasel Ali had been strangled to death and his body left in an area the twins used to play as young boys. Police believed the twins had got into a fight that day over a previous arrest and armed search of their home and Wael Ali had attacked and killed his brother.

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Wael Ali

The case did go to trial with Wael Ali charged with first-degree murder, however, with no DNA evidence or fingerprints, prosecutors had little evidence to confidently place Wael at the scene of the murder. The jury failed to reach a verdict and Wael was set free with a decision made not to try him again. Tragically, two years later, Wael Ali was shot dead in an accidental shooting and his family laid him to rest next to his twin brother.

While the DNA sequences of identical twins are identical, their fingerprints are not, giving investigators one method of accurate identification. Fingerprints are not fully controlled by genetics and the reason we all have different fingerprints, including identical twins, is that the shapes, ridges, and patterns defining each print are developed within the womb influenced by the movement, different positioning and developmental mechanisms of each foetus as it develops. This, however, is no use to investigators if no viable fingerprints are found at a crime scene which can be tested, looping their investigation back to reliance on DNA evidence.

This conundrum of distinguishing the DNA of identical twins has prompted scientists to try and develop reliable technologies which could be used by criminal investigators and there have been some breakthroughs.

In September 2014, the Suffolk County District Attorney’s Office in Massachusetts announced in a press release they had made an arrest in a case previously unresolved due to the suspects in the case being identical twins. In 2004 two women were attacked nine days apart with both women being abducted and sexually assaulted. DNA evidence was retrieved which matched the DNA profiles of identical twin brothers Dwayne and Dwight McNair. With no way to determine which of the brothers carried out the attacks, police were unable to bring charges.

A new forensic technique which specifically targets identifying differences in the full genetic sequences of identical twins was reported in a research paper published in the journal Forensic Science International. In it, researchers reported that as twins age there are minute mutations within their genomes, mutations that appear during the aging process influenced by each individual’s lifestyle. These mutations, if looked for close enough, can be used to genetically pinpoint differences in the DNA of identical twins and provide scientific evidence of which twin a known DNA sample belongs to.

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Dwayne McNair

Circumstantial evidence in this case pointed to Dwayne McNair as the perpetrator and after contacting researchers and paying for the new scientific testing to be carried out, the results indicated “Dwayne McNair was 2 billion times more likely to have been the source of the DNA evidence than his brother”. With this evidence, Dwayne McNair was indicted by a Grand Jury and held on bail. Earlier this year, Boston news station WBUR reported that the District Attorney did not win his battle to have these results included within the upcoming rape trial of Dwayne McNair.  The scientific technique is too new and not backed up with supporting research to its accuracy and reliability the judge ruled and McNair remains in jail awaiting trial.

Marios Savvides from Carnegie Mellon University in Pittsburgh has developed a computer program which analyses the facial features and specifically the facial lines of identical twins and the micro differences in these that can develop as the twins age. A technology these researchers claim is 90% accurate in distinguishing between the faces of identical twins could prove valuable in cases where photographic or video evidence is available of an individual carrying out a crime who happens to be an identical twin.

In most cases of crime which involve identical twins, willful deception is not usually part of the equation. In 1993 a case came to light where a set of identical twins had purposefully switched identities, where one twin claimed responsibility for crimes the other twin had committed and served jail time in their place. On 19 July 1993, Brenda Anderson was attacked just outside her home by her ex-husband, Ronald Anderson, who strangled her until she was unconscious. Ronald was arrested by police hours after the attack, however, at that time, as far as the police were concerned, this same Ronald Anderson was already behind bars serving a six-month sentence for an earlier attack he had carried out on his ex-wife.

According to the LA Times, it was a friend of the twins who enlightened the police. It was Donald Anderson police had in prison for the assault. They said, Donald’s identical twin brother. Ronald Anderson, according to his twin, was having marital problems and abusing substances when he attacked his wife the first time. Donald did not want to see him in further trouble and felt he could handle jail better so he took his place. In what is thought to be the first case of its kind, Donald Anderson turned himself into police in place of his identical twin brother and accepted the six-month prison sentence handed down. Police had no reason to double check the identity of the man they believed was Ronald Anderson and the twin’s deception went unnoticed.

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After Ronald Anderson was arrested for the second attack on his wife and the conspiracy was discovered, an innocent Donald Anderson was released from prison and Ronald Anderson, the true perpetrator, was charged with attempted murder, robbery, and spousal battery.  In January 1994 Ronald Anderson was sentenced to 14 years in jail, jail time that this time his twin brother could not do for him.

Developments in forensic science, crime scene analysis and specifically DNA profiling have been invaluable for the criminal justice system both in prosecuting offenders and eliminating those who are innocent. When unique forensic evidence belonging to an individual is left behind at a crime scene it is very difficult for that individual to claim they weren’t there.

When this evidence, however, is not unique, its power of placing an individual at a crime scene and proving their contact with a victim is greatly diminished. While criminal cases involving identical twins are rare, until science is able to fill this void and further address the issue of identical DNA, these cases will continue to prove challenging, enabling perpetrators of crimes to evade justice.