Having a twin can be an easy way out for suspects.
In the French press, experts commenting on the Marseille twin case were quoted saying that the DNA technology required would be too costly: hundreds of thousand of euros, even millions were some of the numbers mentioned. Hampikian and Richards both disagree, saying it would be in the tens of thousands of dollars. In these cases, labs can't rely on standard FBI DNA tests, because the regions those tests evaluate would be identical for monozygotic twins. They would need to do a whole genome sequencing, says Hampikian, which now costs about $10,000. Hampikian adds that for better results, this would have to be combined with a study of methylation, chemical marks on the DNA that change with the environment (after birth, twins are exposed to different environmental conditions). However, there are no guarantees that differences will be found.