Comparing Fingerprints: What’s The Point?

Fingerprints, simply put, are the impression of friction ridges located on the surface of the fingers. It is the duty of fingerprint examiners to compare certain characteristics of a suspect’s fingerprint, known as points of identity, or minutiae, to points on fingerprints found at the scene of a crime. This comparison can prove that the suspect had, at some point in time, been at that particular scene. A fingerprint match alone does not, however, prove the suspect committed the crime.

Basic Ridge Characteristics

Basic and composite ridge characteristics

Minutiae Minutiae
ridge ending bridge
bifurcation double bifurcation
dot trifurcation
island (short ridge) opposed biurcations
lake (enclosure) ridge crossing
hook (spur) opposed bifurcation/ridge ending

There are as many as 150 ridge characteristics (points) in the average fingerprint. So how many points must a fingerprint examiner match in order to safely say the prints are indeed those of a particular suspect? The answer is surprising. There is no standard number required. In fact, the decision as to whether or not there is a match is left entirely to the individual examiner. However, individual departments and agencies may have their own set of standards in place that requires a certain number of points be matched before making a positive identification.

Examiners make their determination based on he clarity of the print, the uniqueness of the print’s formations, and the examiner’s ability (or lack of) and experience. A less experienced examiner should match as many points as possible, whereas an examiner with many years of experience may settle on as few as a half dozen points that match.

Obviously, the more points that match the better the case for the prosecution.

The FBI maintains the IAFIS system (Integrated Automated Fingerprint Identification System), which is a database containing the prints of 55 million subjects. Police agencies can typically expect to receive responses from the IAFIS system is as little as two hours. This is a sharp contrast to the wait time of three months of just a few years ago.

The IAFIS system is available 24 hours a day, 365 days a year. The system is so quick that officers are able to run a check on a subject’s prints while they are in custody. In the past, officers were often forced to let suspects go only to learn later that they were wanted for crimes in other jurisdictions.

*Photos by Patti Phillips

20 thoughts on “Comparing Fingerprints: What’s The Point?

  • Terry

    Lee, it’s my understanding that even after a ‘hit’ from IAFIS, a human being still must verify which of the perhaps two dozen ‘possibles’ come back in the report (which does not include a nifty computer screen with a photo of the suspect and what he ate for breakfast).

    Also, I was surprised when I started doing research for my books, to discover there isn’t one ‘master’ fingerprint database. I think a lot of readers assume what I did. That if you ever had your fingerprints taken anywhere, at any time, for any reason, they will show up when the cops do a search.

  • Elena

    Being human I, of course, had to peer at my fingerprints. The results brought up a question. Could fingerprints be identified well enough for legal purposes 40 or 50 years after they were taken? We will posit extremely clear prints to work with.

  • Lee Lofland

    Terry – True. The AFIS/IAFIS system sends back a list of possible matches (10-12) and those prints must be examined by hand and eye.

    There is a master fingerprint database maintained by the FBI. That’s the IAFIS system. The database has approximately 55 million prints on file. Even before the system was electronic, the FBI maintained the database. It was slow, but it worked, sometimes.

    But you’re right. Not all prints go into the FBI’s system. They must be submitted to the FBI by law enforcement. If you were printed for employment purposes or when you conducted a real estate transaction, then no, those prints aren’t in the criminal database. However, those prints could be used for identification if you ever do decide to commit a crime.

  • Lee Lofland

    Elena – Prints taken by law enforcement using the ten print cards are quite legible as long as the paper they’re on holds up. I’ve seen many where the cards had yellowed with age (in our old files) and the prints were fine. Just like the day they were taken.

  • Terry

    Lee – follow up. I was printed in California back in the 60’s for a teaching job. I was printed recently by my local Sheriff’s Office as part of their Civilian Police Academy Alumni/Volunteer program. If I moved to Colorado and committed a crime, could they find me via my prints? If so, how? Around here, people complain that they have to be reprinted every time they move from one job to another that requires fingerprinting (usually at their own expense). Hubby was fingerprinted at our Sheriff’s Office as well, using Live Scan, but he has to submit another set of prints if he wants to apply for a concealed carry permit.

  • Lee Lofland

    Terry – When people are printed as part of a pre-employment background check their prints aren’t entered into the system. Instead, they’re checked to see if you’ve been convicted of a crime or are a wanted person. The same is true when people attend citizen’s police academies.

    The fact that your prints are not entered into the system is the reason why people must submit new sets of prints for each job.

    So, no, those prints wouldn’t be on file in the FBI system. However, if they’re saved at the local level for whatever reason, such as in California people submit thumbprints during real estate transactions, then those prints are a permanent record. If police suspect you of a crime they could obtain a copy of that print for identification purposes.

    The only prints in the IAFIS system are those of criminals.

  • Sarah Grimm

    Yup, I looked at my thumbs. I discovered that I must have been swimming while in utero, because there’s a definate current around my islands. VBG

    I have yet to be fingerprinted, even when I attended the local citizen’s police academy. But I’m sure I left a few fingerprints in the last few craft projects I helped my kids with.

  • Terry

    Lee — me, being a pest.

    You said: If police suspect you of a crime they could obtain a copy of that print for identification purposes.

    How do the cops know where to look? I figured if they knew a suspect had been in the military, they could check those records. Of course, I suppose if you have a physical suspect, not just prints, you can figure out by asking the right questions.

    But in fiction, they’ll show a cop finding a print and then being able to figure out who it belongs to even if the person doesn’t have a record.

  • Lee Lofland

    Terry – Right. If they have a suspect in mind they’ll begin a through investigation – asking questions, checking utility records, driver’s licenses, vehicle registrations, deeds, loan documents, liens, marriage records, divorce records, name searches in law enforcement databases, criminal history, post office, school records, banking records, credit cards, etc.

    But learning someone’s identity based on a fingerprint that’s not in the system is fiction.

  • Terry

    Thanks, Lee.

  • Lee Lofland

    Sarah – You’d be surprised to learn how many places you’ve left your fingerprints. You’d be even more surprised to learn where!

    One favorite place to retrieve a male’s finger and palm prints are on the wall behind the toilet. Many men are “leaners.”

    Terry – That’s what the blog is for, so please ask away. If I don’t know the answers I know plenty of people who do. In fact, one of my advisers and a consultant for the fingerprint chapter in my book is a top fingerprint examiner with many years of experience.

  • Sarah Grimm

    Lee – I should have been more clear in my typing, as I meant visible prints where I could study my islands and bifurcations. Ha, dad would be proud, I used a new word in a sentence today!

    I didn’t know that you can receive responses from IAFIS in two hours now. Good to know. I did know that it gives more than one match, and I chuckle whenever I watch television and a definate match will come up on their search. Ever notice that the computer usually lists it as a 100% match? LOL

  • Lee Lofland

    Sarah – I knew what you meant.

    Oh, depending on which day of the week the prints are sent for matching, the results could come back in just a few minutes. Obviously, Mondays would be the busiest day of the week for the system due to investigators submitting mountains of prints from the previous weekend’s crimes.

    Yep, I, too, love it when the match comes back along with the guy’s address, phone number, place of employment, shoe size, and favorite food. IAFIS is not a dating service computer. It can only send back the information it has, which is limited.

  • Sarah Grimm

    Question: With the new fingerprinting of school children that can be done with the parents permission, should the parent allow the police to hold onto the prints, where are they kept?

    If a child goes missing, do the prints of the missing child wind up in IAFIS or some other place?

  • Lee Lofland

    Normally, the parents keep the records. Some departments use a Biometric SecureTouch Fingerprint Device which operates like a small AFIS terminal, to record prints. They also take a digital photo of the child, record height, weight, eye and hair color, race, and whether or not the child wears glasses and/or braces. The family dentist’s name and phone number is also recorded, if possible. All this information is transferred to a disc and given to the parents. Some departments still use the standard ten print cards for rolled (ink) prints.

    Then, in the case of an emergency, parents can provide police with a copy.

    There are home kits available for parents who’d rather do the fingerprinting and photography in the privacy of their own homes. These are for those people who refuse to allow their children to be fingerprinted by the police or other authorities.

  • Sarah Grimm

    I asked because when it was offered in my area, the police department used standard ten print cards but allowed the parent to choose whether they took the cards home or left them which the officers. I’m assuming then that the local department would keep them somewhere?


  • Lee Lofland

    Yes, I’m sure they have a file set up just for this purpose. We did. But, surprisingly, the majority of the parents preferred to hang on to the cards. They didn’t want the police to have a copy.

  • queenofmean

    Lee – thanks, yet again, for an informative post.
    Funny this should come up now. Just the other day, I was looking for something else & came across fingerprints the police did when my son was 5. It was a long time ago, but I don’t think we were given the option of having the police keep them.

  • Elena

    I wasn’t clear with my question – when I looked at my fingers it became obvious to me that the years have put a lot of wear and tear on my fingertips. That’s what got me to wondering if I could be a successful match today against prints that were taken by the FBI in the early 60’s. Or after enough years are there too many changes to the original flow of lines?

    I’m sure they still have them – hope springs eternal.

  • Lee Lofland

    Elena – Yes, your prints are still the same. Normal wear and tear and even sandpapering won’t alter the patterns.

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