How Familial DNA Searching Works, and Where It Is Allowed

On April 28, 2010, California's state DNA lab ran a crime scene profile from the Los Angeles serial killings known as the Grim Sleeper case through its offender database a second time. The first try, in November 2008, had found nothing. This time the profile came back close to that of a man convicted the year before on a felony weapons charge, close enough to suggest a parent and child. Police arrested his father, Lonnie David Franklin Jr., on July 7, 2010. In May 2016 a jury convicted Franklin of 10 murders.

That technique is familial DNA searching. The National Institute of Justice describes it as an additional search of a law enforcement DNA database, run after a routine search finds no match, to develop leads on close biological relatives of the person who left DNA at a crime scene. It rests on a simple fact: first-degree relatives, a parent, child or full sibling, share more of their DNA markers than unrelated people do.

Not the same as genetic genealogy

Familial searching is often confused with investigative genetic genealogy, the method that identified the Golden State Killer. They are different tools. Familial searching uses the government's own databases of convicted offenders and, in some states, arrestees, and the standard forensic markers stored in them. Genetic genealogy uses consumer databases where people uploaded their own ancestry results, reads hundreds of thousands of markers, and can reach second and third cousins. Familial searching is limited to close relatives who are already in a state database.

How a search runs

Arizona's state crime lab publishes a plain description of the process. Software compares the unknown profile against every offender and arrestee profile and ranks the people most likely to be close relatives. The lab then runs additional male-line Y-chromosome tests on the male candidates and full testing on any who remain, narrowing the list to a few names or to none. Arizona accepts only cases with a full DNA profile from an unknown male, an unsolved violent crime against a person, other leads exhausted, and a significant public safety concern.

A name from that process is not an arrest. Investigators still have to find the actual offender among the relative's family and get a direct DNA sample to compare. The Arizona lab put the nationwide success rate at 10 to 15 percent of searches as of March 2021.

The Llandarcy murders

One of the earliest uses came from Wales, before most American states had any policy on it. On Saturday, July 14, 1973, 16-year-old Sandra Newton disappeared after a night out in Briton Ferry. She was found raped and strangled near Tonmawr. Two months later, on September 16, 16-year-olds Geraldine Hughes and Pauline Floyd were found raped and strangled in woodland at Llandarcy after accepting a lift home from Swansea. Witnesses described a white Austin 1100.

Detectives questioned thousands of owners of that model. One was Joseph Kappen. When police spoke to him, his Austin 1100 was on blocks with its wheels removed, and his wife gave him an alibi that later proved false. The investigation was scaled down in 1974.

In 1998 scientists recovered a DNA profile from the clothing of Hughes and Floyd, and in 2000 it was searched against the UK database without a match. A reinvestigation, Operation Magnum, narrowed thousands of names to a priority list of 500, with Kappen at number 200. When detectives went to his Port Talbot address in August 2001, they learned he had died of lung cancer in June 1990.

South Wales Police then looked for relatives of the killer in the database. Kappen's son Paul, a car thief whose DNA was already on file, came back with a distinctive similarity to the crime scene profile. Kappen's body was exhumed in 2002, and forensic testing matched him to the murders. Police named him as the killer. He was never charged or tried because he had been dead for 12 years.

The first New York City case

On February 24, 1999, 13-year-old Minerliz Soriano was last seen walking home from school in the Pelham Parkway section of the Bronx. Four days later her body was found wrapped in a trash bag in a dumpster behind a video store in Co-op City. She had been sexually abused and killed by compression of her neck. Semen stains on her sweatshirt produced a DNA profile that matched no one.

New York adopted familial search regulations in October 2017. In April 2019 the NYPD and the Bronx District Attorney's Office applied for a familial search, and the state database returned a link to the late father of the eventual defendant. Several relatives were ruled out. Investigators then focused on Joseph Martinez, who had been 27 and living in Minerliz's building in 1999, and who was known as Jupiter Joe because he taught astronomy to children. Police covertly collected his DNA, and it matched the sweatshirt.

Martinez was arrested on November 29, 2021, and pleaded not guilty. On November 14, 2025, a Bronx jury convicted him of two counts of second-degree murder. On March 26, 2026, he was sentenced to 25 years to life. The Bronx District Attorney called it the first case in New York City solved with familial DNA.

The legal ground under that case shifted while it was pending. In 2022 a state appellate court struck down New York's familial search regulations, ruling that the agencies that wrote them had exceeded their authority. On October 24, 2023, the New York Court of Appeals reversed that decision and held that the state's forensic science commission did have the power to allow familial searches.

A 1995 Brooklyn case

On August 2, 1995, a 36-year-old woman was forced at gunpoint onto the roof of a building on Pulaski Street in Bedford-Stuyvesant, raped and robbed of her jewelry. A rape kit was collected at Brooklyn Hospital, but the DNA matched no one. In June 2005, before the statute of limitations ran out, prosecutors indicted the unknown man by his DNA profile.

According to the Brooklyn District Attorney's office, advances in familial DNA technology produced a person of interest in the summer of 2026, and an abandonment sample confirmed his DNA matched the rape kit. On September 18, 2026, William Stephens, 54, of the Bronx, was arraigned on charges including first-degree rape and robbery, and bail was set at $250,000. He is presumed innocent, and his next court date was set for October 30, 2026.

Where it is allowed

California became the first state to adopt a familial search program, in 2008. As of March 2021, according to the Arizona lab, 16 states had active programs: Arizona, California, Colorado, Florida, Kentucky, Louisiana, Michigan, Minnesota, New York, North Carolina, Ohio, South Dakota, Texas, Virginia, Wisconsin and Wyoming. Maryland and the District of Columbia ban familial searches of police databases. Montana since 2021 has required a warrant for familial or partial match searches.

What the database can and cannot see

Familial searching can only find relatives of people the state has already collected DNA from. The FBI's CODIS program began as a pilot in 1990, and the national index did not go live until October 1998, so older cold cases rely on whoever has entered state databases since. Kappen was found because his son stole cars.

That same feature is the main objection to it. Critics, including the Legal Aid Society in New York, argue that because police databases over-represent people from heavily policed communities, familial searching puts their relatives under suspicion far more often than other families. Labs that run the searches, such as Arizona's, limit them to unsolved violent crimes where every other lead has been exhausted. Both points describe the same thing: the search is only as wide, and as narrow, as the database it runs against.

Sources

1. National Institute of Justice: Familial DNA Searching, Current Approaches (2015)
2. California Attorney General: Brown's forensic experts identify Grim Sleeper suspect through familial DNA (July 8, 2010)
3. NBC Los Angeles: Lonnie Franklin Jr. convicted in Grim Sleeper serial killings (May 5, 2016)
4. Arizona Department of Public Safety: Familial DNA Analysis fact sheet
5. Joseph Kappen - Wikipedia
6. Bronx District Attorney: Joseph Martinez sentenced to 25 years to life for 1999 murder of Minerliz Soriano (Mar. 26, 2026)
7. Murder of Minerliz Soriano - Wikipedia
8. Matter of Stevens v. New York State Division of Criminal Justice Services, N.Y. Court of Appeals (Oct. 24, 2023)
9. Brooklyn District Attorney: Bronx man arrested for 1995 gunpoint rape on Bedford-Stuyvesant rooftop (Sept. 18, 2026)
10. EFF: Maryland and Montana pass the nation's first laws restricting genetic genealogy searches (2021)
11. Legal Aid Society: Court rules NYS law enforcement must end familial DNA searches (May 2022)
12. Southern California Law Review: Familial DNA and Due Process for Innocents (July 2025)

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