Tag Archives: Familial searching

Rhode Island arrests man following a partial match

A Rhode Island newspaper reports that “[t]he Cranston Police Department has arrested 49-year-old David Finegan, of no permanent address, for the burglary and sexual assault of an 81-year-old woman.” [1] Police “collected [DNA] at the crime scene on May 2.” On June 10, the Rhode Island Department of Health reported that it had a DNA profile from the crime with which to query an offender database. The Rhode Island laboratory did not use software designed for kinship searching, but on July 8, the department advised detectives that it had found a partial DNA match to a female inmate.

The article does not speculate on why it took a month to complete a routine computer search and report the results.Was it because of legal concerns? Was the partial match trawl intentional, or was the discovery inadvertent? Whichever it was, the detectives turned their attention to five male siblings. They discovered that one of them, David Finegan, was “in close proximity . . . on the night of the incident.”

Why this roundabout method of identifying Finegan? He was on parole in July. Was the underlying offense not one that triggered entry into the DNA database? Was there a backlog in entering offender profiles into the database? Whatever the explanation, Finegan had the misfortune of being picked up on July 14 on a parole violation and held for the weekend. Detectives quickly obtained a search warrant and took a sample of DNA from him before he made bail and dropped out of sight. A week later, they learned that it matched the crime-scene DNA.

Pursuing an anonymous tip, police found and arrested Finegan in Providence. He “is being charged with burglary and first-degree sexual assault.” Interestingly, he has an arrest record (including domestic assault, felony DWI, resisting arrest and other assaults) dating back to 1991. A bill that would expand the state database to include arrestees is before House and Senate committees in Rhode Island.


1. Joe Kernan, Arrest Made in Rape of Elderly Woman, Cranston Herald, Dec. 19, 2011


Thanks to Frederick Bieber for informing me of the Cranston Herald article.

Update on Pennsylvania Senate Bill 775

By a vote of 42-6, the Pennsylvania Senate passed a bill (discussed here on March 18, 2011) to begin taking DNA samples on arrest and to authorize kinship trawling in some cases. The proposed changes come with a price tag. Although the state police laboratory is reducing the backlog of convicted-offender samples, it hardly has surplus capacity. The appropriations committee’s fiscal note estimates the cost for laboratory staff and supplies for phasing in just a portion of the samples that could be collected from arrested at more than $560,000 in 2012-13.

Legislation to Implement Kinship Matching

A few years ago, “Jeffrey Rosen, a constitutional law professor at George Washington University, warned: ‘I can guarantee if familial searching proceeds, it will create a political firestorm.'” (1) But familial searching, as it is tendentiously called, prompted no huge political protests when California, Colorado, New York, and Virginia adopted it administratively. Now, legislative initiatives to implement it in various states (2, 3) and federally (4) have begun. However, the proposed legislation is timid, usually authorizing the practice only in murder and sexual assault cases and only after traditional investigative methods have failed.


1. Maura Dolan & Jason Felch, California Takes Lead on DNA Crime-fighting Technique: The State Will Search its Database for Relatives of Unidentified Suspects in Hopes of Developing Leads, Los Angeles Times, Apr. 26, 2008

2. Mike Cook, DNA — It’s All in the Family, Minnesota House of Representatives Session Weekly: News from the House, Apr. 8, 2011

3. Mark Scolforo, DNA Proposal Has Foes: Pa. Bill to Expand its Collection Opposed by the ACLU, Phil. Inquirer, Oct. 2, 2011

4. Press Release, Schiff’s Familial DNA Language Passes as Part of Conference Report, Nov. 21, 2011

An Odd Set of Odds in Kinship Matching with DNA Databases

The 22d International Symposium on the Future of Human Identification began yesterday with a set of workshops. One was on “familial searching.” The phrase refers to trawling the profiles in a DNA database for certain types of partial matches to a DNA profile from a crime-scene sample.

Partial matches that are useful in generating investigative leads to family members arise much more often when a particular kind of relative (say, a full sibling) is the source of the crime-scene sample than when an individual who is not closely related to the database inhabitant is the source. The ratio of the probability of the partial match under the former condition (a given genetic relationship) to the latter (unrelated individuals) is a likelihood ratio (LR). The LR (or, technically, its logarithm) for siblingship expresses the weight of the evidence in favor of the hypothesis that the source is full sibling as opposed to an unrelated individual.

After explaining the this idea, the first speaker presented the following formula:

“Odds” = LRautosomal x LRY-STR x 1/N         (1)

She attributed this formula to the California state DNA laboratory that does familial searching in that state. In this equation, N is the size of the database, LRautosomal is the likelihood ratio for the partial match at a set of autosomal STR loci, and LRY-STR is the likelihood ratio for the matching Y-STR haplotype.

She described this as a Bayesian computation that could lead to statements in court such as “there is a 98% probability” that the person whose DNA was found at the crime scene is a brother of Joe Smith, a convicted offender whose DNA profile is in a DNA database.

There are three interesting things to note about these suggestions. To begin with, it is not clear why such a statement would be introduced in a trial. By the time the suspect has become a defendant, a new sample of his DNA should have been tested to establish a full match to the crime-scene sample. At that point, why would the judge or jury care whether defendant is related to a database inhabitant. The relevance of the DNA evidence lies in the full match to the crime-scene sample, and the jury need not consider whether the defendant is a relative of someone not involved in the alleged crime. (One might ask whether the trawl through the database somehow degrades the probative value of the full match, but, if anything, it increases it. [1])

The issue could arise, however, if police were to seek a court order or search warrant to collect a DNA sample from the suspect. At that point, they would need to describe the significance of the partial match to the convicted offender.

This possibility brings us to the second noteworthy point about equation (1). The “odds” (or the corresponding probability) are not the way to present the weight of the partial match. Consider the prior probability of a match in a small database, say, of size N=2. Prior to considering the partial match, why would one think that the probability of a database inhabitant being the sibling of the criminal who resides outside the database is 1/N = 1/2? It is quite improbable that the database of two people includes a relative of every criminal who leaves DNA at a crime-scene. The a priori probability for a small database must be closer to 0 than 1/N.

That the prior probability is less than 1/N is a general result. The only exception occurs when it is absolutely certain that a sibling of the perpetrator is in the database. On that assumption, prior odds of 1 to N-1 are not unreasonable. But that assumption is entirely artificial, and to advise a magistrate that the posterior odds have the value computed according to (1) would be to overstate the implications of the partial match.

The third thing to note about dividing by N is that it accomplishes nothing in producing a viable list of partially matching profiles in a DNA database trawl. The straightforward approach is to produce a short list of candidates in the database whose first-degree relatives might be the source of the crime-scene sample. The minimum value of LRautosomal x LRY-STR should be large enough to keep the two conditional error probabilities (including a candidate when there is no relationship, and not including a candidate when there is a relationship) small. This threshold value does not depend on N. (A later speaker made this observation.)

Equation (1), it seems, is useless. Instead, the magistrate should be told the value of the LR and how often such large LRs would occur when a crime-scene sample comes from a relative versus how often it would occur when it comes from an related person.


1. David H. Kaye, 2009, Rounding Up the Usual Suspects: A Legal and Logical Analysis of DNA Database Trawls, North Carolina Law Review, 87(2), 425-503.

More on Pennsylvania Senate Bill 775

The Pennsylvania Senate Judiciary Committee held a hearing on DNA evidence issues today. The attached statement submitted to the committee discusses the provisions of SB 775 on taking DNA from arrestees, on kinship trawling (called “modified DNA matching” in the bill), and on the release of DNA anonymized profiles for research.

How Successful Are Kinship Searches (aka Familial Searches)?

Kinship analysis refers to comparing DNA profiles from different individuals to see if one individual might be a close relative of another. It is done all the time in child-support and missing-remains cases. It is done in criminal cases when a rape victim has a child or aborted fetus.

Using the same principles of genetics, kinship searches can be conducted in a law enforcement database of identifying DNA profiles. For brevity, we can call the convicted offenders (or, in some jurisdictions, arrestees) whose DNA profiles are recorded in a database “database inhabitants.” The profile derived from a crime-scene can be compared with all the database profiles to see (1) if a database inhabitant’s profile is an exact match (the usual “cold hit”) or (2) if there is a close enough match (as shown by kinship analysis) that the crime-scene DNA may have come from a very close relative of a database inhabitant. One group of scientists (Bieber et al. 2006) estimated that kinship matching could generate thousands of useful investigative leads nationally. However, the technique is almost never used, leaving proponents and opponents to rely on their choice of anecdotes about its value and accuracy.

A case in point is a recent law review article that emphasizes “one revealing fact: [Denver’s District Attorney, Mitch Morrissey‘s] familial searches did not work. None of the three matches turned out to point toward a relative, much less the source, of the actual crime-scene sample. . . . [I]t failed in three separate cases . . . .” Erin Murphy (2010).

However, these searches did not use a matching strategy designed and optimized to detect kinship. According to Moreau-Horwin (2011):

In 2009, Morrissey launched a familial search research project with the Denver Police Department. A familial search software program was designed by the DA’s office and the Denver Police Crime Lab. The program would only extend to siblings and parents. When a hit is made, family members could not be questioned unless investigators isolate a suspect using traditional detective work.

This software program resulted in the first case ever to use a deliberate familial search in the United States. In February 2008, several cars were burglarized in a Denver apartment complex. In one car, blood stains were left on the front seat. After extracting the DNA profile, the police ran it through the DNA database, but did not get a match. They then processed the sample as a familial search and a brother of the offender was identified. This led law enforcement to 21 year-old, Luis Jaimes-Tinajero. Police received a court order to take his blood and it was a perfect match to the evidence sample. Jaimes-Tinajero pleaded guilty on September 10, 2009 to criminal trespass and was sentenced to two years probation. Although this case was only designed to test the new familial search software, it would probably have received more publicity had it led to the arrest of a rapist or murderer and not a car burglar who apparently stole only $1.40 in change. 1/

So, is Morrissey’s record 0 for 3 or 1 for 1? It is neither. Surely, there were many cases in which the Denver kinship searches drew blanks or false leads. But the usual, full-match searches do not always produce cold hits either. The latter hit rate depends on the fraction of perpetrators of the crimes who are “database inhabitants.” The former hit rate is much more complicated. It depends on (1) sensitivity–that is, the ability of the kinship matching algorithm to hit on a true relative of the crime-scene profile source in the database; and (2) prevalence–the proportion of relatives of database inhabitants (a) who commit crimes with DNA traces and (b) who are not themselves database inhabitants. The sensitivity of various algorithms can be estimated (Bieber et al. 2006; Curran & Buckleton 2008), but the prevalence is more uncertain. The known fact that the prison population contains a substantial fraction of close relatives is high might mean that there are many more as yet unidentified relatives engaged in criminal activities. (Bieber et al. 2006).

Until a state implements a well designed form of kinship matching in a large number of cases, however, the real-life efficacy of the technique will not be known. The only reference I have seen so far to such information is in a news report of a study in the United Kingdom which “found that, out of 100 searches, more than a dozen led to a suspect.” (Miguel 2007).


1. Ms. Moreau-Howin is a forensic DNA database consultant who maintains a website, DNAforensics.com. For more details on the successful case from a traditional news source, see 9News.com, Car Vandal Nabbed Thanks To Brother’s DNA, Nov. 16, 2009, http://www.9news.com/rss/story.aspx?storyid=127140 (reporting that Luis Jaimes-Tinajero’s “brother was in the system because of a felony conviction for auto theft” and that the “car was one of many at his Denver apartment complex broken into [that] morning”).


9News.com, Car Vandal Nabbed Thanks To Brother’s DNA, Nov. 16, 2009, http://www.9news.com/rss/story.aspx?storyid=127140, last accessed Feb. 20, 2011

Frederick R. Bieber et al., Finding Criminals Through DNA of Their Relatives, 312 Science 1313 (2006).

James M. Curran & John S. Buckleton, Effectiveness of Familial Searches, 48 Sci. & Justice 164 (2008).

Ken Miguel, The controversies surrounding ‘partial DNA,’ ABC7 News, Nov. 13, 2007, http://abclocal.go.com/kgo/story?section=news/drive_to_discover&id=5760664, last accessed Feb. 20, 2011

Raphaele Moreau-Horwin States Using Familial Searches, http://www.dnaforensics.com/StatesAndFamilialSearches.aspx, last accessed Feb. 20, 2011

Erin Murphy, Relative Doubt: Familial Searches of DNA Databases, 109 Mich. L. Rev. 291 (2010).