BOSTON -- A powerful forensic search tool known as familial DNA is gaining clout for its ability to identify suspects when all else fails.

Recently adopted in the state of Virginia and under consideration in Pennsylvania, the controversial search technology is used in Colorado and California, where it was credited with nabbing suspects in serial murders.

In familial DNA searches, authorities collect crime scene DNA and search for a near -- but not perfect -- match with existing DNA in the criminal database, presumably from an incarcerated blood relative of the yet unknown suspect.

A near match may cause authorities to focus on a potential suspect, possibly the first break in a protracted investigation that otherwise has no leads.

"It will give critical investigative leads in the most serious cases that are not otherwise going anywhere," said Carll Ladd, supervisor of the DNA division of the Connecticut state forensic lab.

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Ladd pointed to a "text book case" where familial DNA could have been used, citing the East Coast Rapist, who is connected by DNA to 12 of 17 attacks from Virginia to New England.

With no arrest in 14 years, authorities in March charged a suspect in the serial rape case after following him and collecting his DNA on a discarded cigarette butt.

Ladd said that an arrest may have been possible sooner if a familial DNA search had been conducted -- and if the suspect had a family member in a state database.

In fact, Virginia prosecutor Paul Ebert said investigators told him the East Coast Rapist suspect actually did have a relative imprisoned in Connecticut and may have had DNA in the system.

But familial DNA searching is not yet approved as a tool in Connecticut or Rhode Island, where attacks took place, and is prohibited in Maryland, where other victims were raped. Virginia's decision to search with familial DNA was announced after the East Coast Rapist's arrest.

Advocates tout familial DNA as the next practical step in maximizing the use of DNA, in a responsible manner, to solve crimes. They say familial DNA searching should be used only when all other investigative tools have been exhausted and only in the most serious cases.

Even then, say critics, the search technique could infringe on privacy, unfairly target innocent people and disproportionately affect African Americans and Hispanics, the largest populations in the database.

Some opponents also say the DNA database was created only to determine perfect matches among the 9.4 million offender profiles currently on record nationally or to link DNA in a series of crimes, not for partial identification.

But using pieces of information -- a partial license plate or the color of a car-- is already regularly employed in police work.

"This is using partial information, a close but not perfect match, as an investigative lead.  It alone is not used as a basis for a conviction," said Dr. Frederick Bieber, a professor of pathology at Harvard Medical School.

Bieber said familial DNA searches could prove more efficient, less intrusive and more cost effective than some more traditional investigative methods.

Solving a crime faster by using familial DNA also means immediate exoneration of others and fewer potential victims, said Chris Asplen, a former federal prosecutor with a special focus on forensic DNA technology and its use in the courts.

Legal experts, including Asplen, say passing specific legislation to enable familial DNA search isn't necessary. The search technique is taking what was already legally obtained by law enforcement and using it "more effectively and more efficiently," said Asplen.

Broad adoption of the familial DNA search remains uncertain given the added cost to some already strained state budgets.