Scientists in Ohio, United States, announced their findings after testing the backlog of rape kits, which were used between 1993 and 2010.
Analysis of the kits – used to collect evidence from the victims of sexual attacks - has given the researchers greater insight into the behaviour of sexual predators.
More than 250 people have already been convicted of sexual offences as a result of the tests and investigators expect the prosecutions to continue.
The Cuyahoga County Sexual Assault Kit Task Force – a multidisciplinary body dedicated to following up sexual assault cases stemming from the untested kits – worked with the Begun Centre for Violence Prevention Research and Education at Case Western Reserve University, who study violence and its prevention, to gain an insight into patterns revealed by the kits.
Starting in 2014, the task force say the discovery that serial rapists are much more common than previous studies have suggested could change the way sexual assaults are investigated.
Of 243 sexual assaults studied, 51 per cent were tied to serial offenders, who tended to have more extensive and violent criminal histories than one-off sexual offenders.
“Our findings suggest it is very likely that a sexual offender has either previously sexually assaulted or will offend again in the future,” said Rachel Lovell, senior research associate at the Begun Centre.
“Investigating each sexual assault as possibly perpetrated by a serial offender has the potential to reduce the number of sexual assaults if investigations focus more on the offender than on single incidents.”
The researchers also found many rapists have long criminal histories, often beginning before their first documented sexual assault and continuing after it. Seventy-four per cent of serial rapists were found to have been arrested before the sexual attack and 95 per cent had been arrested afterwards.
In contrast, for one-off rapists, the figures were 51 per cent and 78 per cent respectively.
The different types of offenders were also found to behave differently during the course of their crimes, the researchers said.
Sexual assaults committed by serial offenders more frequently involved kidnapping victims and threatening them, the researchers found. Serial offenders were also less likely to be known to their victim.
But sexual assaults committed by serial offenders less frequently involved restraining victims and injuring them in order to complete the attack. However, one-off offenders were more likely to punch, slap, hold down or restrain a victim.
One-off offenders were more likely to attack in their own house or the house of the victim. However, 58 per cent of serial offenders committed all of their crimes in the same type of setting, such as a vehicle.
The researchers also said one-off offenders were more likely than serial offenders to commit sexual assaults with others, such as participating in gang rapes.
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