why convicts HATE DNA testing


CODIS, or the COmbined DNA Index System, is the interconnected local, state, and national DNA databases of convicted offender profiles, arrestee profiles, and forensic profiles. 

A convicted offender profile is a DNA profile collected from a person who has been convicted of a crime. Which crimes qualify depends on the state. Some states are “all felons,” where a DNA sample is collected from anyone convicted of a felony. Other states may require a “qualifying offense” such as murder, sexual assault, or other crimes. These samples stay in the database indefinitely.

An arrestee profile is similar to a convicted offender profile in that it is a DNA profile collected from an actual person. This time, the person has not been convicted of a crime, but arrested for the commission of a crime. These profiles must be removed from the database if the charges against the person are dismissed or the person is found not guilty/acquitted.

A forensic profile is a DNA profile that comes from a crime scene and is thought to belong to the perpetrator of the crime. DNA profiles that are found at a crime scene but come from a witness or complainant or victim cannot be entered into the database. In essence, CODIS houses DNA profiles from perpetrators and suspected perpetrators.

And this is how it works:

photo credit: Lauren Paulsen via photopin cc
photo credit: Lauren Paulsen via photopin cc

Let’s say that someone broke into a car by smashing the car window. You find blood on a piece of broken glass where he cut himself. The blood is collected onto a sterile swab (think Q-tip) and sent to the crime lab for testing. The lab obtains a male DNA profile from the blood sample and enters it into CODIS where it is searched against the other profiles in the database. This is a forensic profile.

The forensic profile can either make a case-to-case hit if it matches a crime scene sample from a different case (another forensic profile). This type of hit would link the two cases together. Case-to-case hits are helpful in identifying serial perpetrators (serial burglars, serial sex offenders, serial killers, etc.). Or if an unsolved case hits against a solved case, it could link the unsolved case to a perpetrator. The forensic profile could also match a convicted offender or arrestee profile. This type of hit would provide the name of the person associated with the DNA sample to law enforcement. The officer would then need to collect a sample from that individual and bring it to the lab so that they could confirm the hit and write a report associating the two samples.


photo credit: Johnny Grim via photopin cc
photo credit: Johnny Grim via photopin cc

Processing property crime samples for DNA (burglary, theft, burglary of a motor vehicle, etc.) has reduced crime rates in cities such as Denver. In 2005, Denver did a pilot study to determine the cost-effectiveness of using DNA to process burglaries versus a typical police investigation. Not only was DNA more effective and cheaper, but it led to amazing results. Per the Denver DNA Burglary Project (denverda.org):


  • More than 95 prolific burglars in the Denver area were caught and convicted
  • The burglary rate in Denver dropped 26%
  • The use of DNA evidence in burglary cases results in average 14-year prison term (compared to an average 1.4-year jail sentence for cases without DNA)
  • The project showed that in property crimes, the presence of DNA can be paramount to successful prosecution. In cases that include DNA evidence, the prosecution filing rate is approximately 42%, which is more than eight times the rate of prosecution in cases without DNA evidence.
  • Annual savings to citizens in Denver are estimated at more then $29 million to date.

Of any type of crime, property crimes are the most likely to result in a CODIS hit because burglars are the most likely to be serial perpetrators. Some people make a living off of burglary. “Habitual burglars commit on average more than 240 burglaries a year.”  

The unfortunate truth is that many crime labs don’t have the personnel or budget to process property crimes. They are backlogged and struggle to keep up with personal crime casework (crimes against persons like murder, sexual assault, aggravated assault, aggravated robbery, etc.). But more on that in a future post.

Want to learn more about CODIS? You can visit the FBI’s CODIS page.

Now you: what have you heard about DNA databases?


4 thoughts on “why convicts HATE DNA testing

  1. This is fascinating stuff. If someone had charges dismissed and was set to have their profile deleted, would the deletion be instantaneous? Say a suspect actually commits a crime after he\she was supposed to have their profile deleted, could the information be restored and rechecked against a new crime if the technician thought it was viable?


    1. Great question, TIm.

      The lab gets a court order (signed by a judge) ordering them to expunge the profile. Once the lab receives the notice, it’s an easy thing to pull up the profile and delete it from the database.

      If the suspect committed a crime after the order was signed but before the lab expunged it (say the lab hadn’t received the order yet), and there was a match between the person and another case, I assume the lab would report the match to law enforcement. At that point, it’s more of a legal issue than a laboratory issue. What is admissible in court is up to the legal system, not the lab.

      After the profile is expunged, the laboratory does not keep it hidden away just-in-case. That would be unethical. The profile is gone. It’s like deleting a file from your computer. The lab can’t get it back. Depending on the court order, if the documentation was not ordered to be destroyed, then technically the paperwork would still be in the lab somewhere, but it wouldn’t be in a searchable database.

      The expungement of profiles happens very infrequently – maybe only one or two times in the 11 years I worked at our lab. And I can only remember one time that we were ordered to destroy case records.


  2. Hmm, sounds like a field with a real need and steady future. But is the lack of personell & budget something that could be fixed with more people or is it more of a priority problem with higher-ups?


    1. Another good question.

      Mostly it’s an issue with the administration or government (state or local). Either the laboratory doesn’t have enough people because they haven’t asked for them, or they’ve asked and been refused. A lot of time they don’t ask for enough people–they might not have a realistic expectation of how many people they would need to function at an ideal level.

      At the lab where I worked, we went from a staff of 4 to 44 during the time I worked there. We had a backlog of a couple of thousand cases and went to working cases as they came through the door and reporting them in less than a month. We hired an outside consultant to come in and access our staffing and equipment needs. He made a recommendation, it was taken to our local government, and they agreed to fund the positions over a period of time (10-11 a year). It was a wise decision.

      Most labs don’t work this way. Government labs are run and administered by scientists who may or may not be business savvy. Those labs that are run with an eye towards business, or a good business model, are the ones that are more successful. That’s why some people are pushing to privatize criminalistics. I personally think that’s a bad idea. Government labs can do a good job with the correct oversight, personnel, and budget. With privatizing, you run into what I talked about in my post in crime lab bias. Only processing the samples that aid law enforcement because you’re trying to keep costs down.

      Usually forensic laboratories don’t have open positions for long. It’s not like there’s shortage of people applying for jobs in crime labs. 😉 Unless the crime lab is in an unpopular location or if they pay poorly.


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