In the nearly four months since 30-year-old Howard Beach jogger Karina Vetrano was strangled in Spring Creek Park, teams of NYPD detectives have worked the case with no suspects. The best lead so far has been DNA left on Vetrano’s body that hasn’t matched any profiles in state or national databases of convicted criminals, police said.

But some law enforcement and forensic science experts said an innovative and controversial DNA analysis technique that isn’t used in New York has the potential to bring investigators closer to finding Vetrano’s killer.

The methodology, known as “familial searching,” uses probability rankings and analysis of the Y chromosome to identify people already in the state DNA database who are relatives of the unknown suspect.

Once relatives are identified, police can use traditional investigative techniques — even rummaging through garbage cans — to develop reasonable suspicion and then retrieve a DNA sample from a person of interest.

Philip Vetrano, Karina’s father, said he was astonished to learn it is not used in New York and promised to raise the issue with police and government officials.

“I am going to stop at nothing to have this done,” said Vetrano, who now wants investigators to give it a try.

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While the NYPD collects DNA evidence in homicide cases, police don’t actually test the material. They give it to the city Office of Chief Medical Examiner, which develops a DNA profile. The profile is then sent to the New York State Police, which takes the profile and uses special software to try to find a match with DNA profiles already on file in state and national databases.

The more specialized familial DNA searching, known to professionals by the abbreviation FS, is done in nine states, including California, Texas, Virginia and Michigan, as well as in the United Kingdom and the Netherlands. While most cases analyzed with FS don’t produce suspects, in some celebrated cases — such as the “Grim Sleeper” serial killer Lonnie David Franklin Jr. in California — defendants have been identified, charged and convicted.

A poster offering a $10,000 reward for information leading to the arrest of the person involved in the killing of Karina Vetrano, hangs from a utility poles in Howard Beach on Aug 22, 2016. Photo Credit: Uli Seit

NYPD Chief of Detectives Robert Boyce, through a spokesman, did not want to go into exact details but said the department is trying everything it can to develop a solid DNA lead in the Vetrano case.

“This is the most comprehensive DNA investigation we have done,” Boyce said through spokesman Stephen Davis. “We have done everything we reasonably can do in terms of trying to get expanded DNA out of here.”

But city and state officials have acknowledged that true familial searching is not done in New York State. Instead, the officials said, New York uses a hit-or-miss “partial match” analysis that experts said fails to find matches for siblings in 99.99 percent of the cases.

Such long odds allow only for rare “serendipitous matching,” said retired California prosecutor Rockne Harmon, a vocal advocate nationally of familial searching.

One such chance finding happened in Suffolk County in the case of John Bittrolff, a Manorville man who was arrested in 2014 on murder charges after a partial DNA match led investigators to identify his relatives. Bittrolff, who has denied wrongdoing, awaits trial in the slayings more than 20 years ago of Colleen McNamee, 20, of Holbrook, and Rita Tangredi, 31.

The Suffolk case stemmed from what Harmon called “miraculous luck.” Since June 2011, New York officials have come across 91 partial matches in the state DNA databases. Three cases identified family members of a potential suspect, and there have been two arrests, including the Bittrolff case, state officials said.

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“Partial matching is not even a substitute [for familial searching], it is an ineffective approach to find relatives,” said Prof. Bruce Budowle, director of the Center of Human Identification at the University of North Texas Health Science Center in Fort Worth.

By contrast, familial searching, using special software to compare and rank DNA profiles, would give investigators a more focused, efficient approach, Harmon and Budowle said. The software gives investigators a ranking of likely matching relatives. Then, an analysis of the male Y chromosome may bring investigators closer to actually confirming a relationship.

Officials said the main reason New York doesn’t use familial DNA searching is ambiguity in state laws and regulations governing DNA testing. An official at the city medical examiner’s office said he believed state law doesn’t allow it. A spokeswoman for the state Division of Criminal Justice Services said no law absolutely bars such a process.

However, a state official intimately familiar with the DNA testing said a labyrinth of regulations makes it unclear if familial searching is allowed.

“This is a phenomenal tool,” the state official acknowledged.

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In 2009, when partial matching was authorized in the state, the New York Civil Liberties Union said in a statement the science of partial matching and the potential for human error made it problematic.

“A policy that implicates New Yorkers in a criminal investigation solely because they are related to someone with DNA in the state’s databank is a miscarriage of justice,” NYCLU executive director Donna Lieberman said.

But Harmon and others said that true familial searching doesn’t lead to anyone being charged falsely.

Experts caution that familial searching doesn’t lead to success in every case. A recent report from the National Institute of Justice noted that the success rate in familial searches in California was 39 percent and 26 percent for Colorado.