In the clip above, you see Chelsey Rustad tell about how her DNA pointed out a murderer who was sentenced to life.

The double murder in Linköping in 2004 when an eight-year-old and a teacher were stabbed to death became a pilot case in Sweden for the new method.

The police had DNA from the perpetrator as traces of blood and hair, but despite thousands of tips, interrogations and tipping, no one could be arrested for the crime.

Mass murderers in the United States were found with DNA genealogy

By 2020, the US FBI had managed to solve a cold case with the help of DNA genealogists and searches in commercial databases where people sent blood samples and genetic predispositions to search for their roots.

The so-called "Golden State Killer" was convicted of 13 murders and sentenced to life.

Swedish police wanted to test the same method in the Linköping case.

They managed to extract good enough DNA from the crime scene to be able to test the perpetrator's single-base polymorphisms or "snippets" (single nucleotide polymorphisms) in a commercial genealogy database in the United States.

Snippets are pieces of the genome that can be quickly compared between individuals and if many are the same, they are related.

Based on these distant relatives in the database, it is often possible to look back in the family tree via population registers and church records to a common ancestor and then forward again to a possible perpetrator.

The double murder in Linköping - successful pilot case

The perpetrator in Linköping was not previously in the police register, but on October 1, 2020, he was sentenced for the double murder to forensic psychiatric care.

An investigation after the pilot case proposes that the method should be introduced as a tool for the police in investigations of serious crimes such as murder and rape or when identifying a deceased person and not succeeding with other methods.

- There are definitely both cold cases and other unsolved serious crimes where the tool could come to the rescue.

Hopefully we will get it in sometime during the year, says Ricky Ansell who is an operations expert at the National Forensic Center, NFC.

The police may only search for relatives who have approved it

A challenge with the method is to obtain enough biological material of good quality from a perpetrator to be able to search a genealogy database.

Another challenge is that mainly people from northern and western Europe appear in the commercial genealogical databases, if the perpetrator has other roots, you usually do not get a hit.

The current databases Family Tree DNA and GEDmatch both say that they only let the police search for DNA from users who have given permission for it, which is a few hundred thousand of millions of users.

Decision on the method for New Year

Right now, the police are further investigating whether and how DNA genealogy research can be introduced as an investigation method.

The Privacy Protection Authority must provide a consultation response on whether they see problems with the handling of genetic information in persons who are not suspected of crime.

The police's national operational department states via the press department that a decision on DNA genealogy research will be approved as a method within the Swedish police is expected at the turn of the year 2021/2022.

See more about what our DNA can reveal in the World of Science - The secrets of our DNA on Monday 5 April at 20.00 on SVT2 or on SVT Play.