Forensic Question: DNA Testing Turn Around Time

Amanda asks:

How long does it typically take for DNA results to come back in a murder case, specifically blood on a knife? Could the agency get a preliminary report (i.e. blood type) any faster?

Amryn says:

Each lab will have its own turnaround time for DNA. For most state crime labs or local agency labs (meaning those that are attached to a law enforcement agency) the turnaround time is likely to be several weeks/months. This is because they may receive dozens of cases per day, certainly per week, and cases are usually worked in the order they are received. Some cases may only have one or two samples that need DNA testing, while others may require 40 or 50 (this is not as common, but not unheard of either.)

In some cases, a district attorney or someone in charge of the lab may declare the case a “rush” or an “expedite” (usually documented in the form of a letter), in which case it jumps to the front of the line. A lab may drop everything else to work on this case, depending on the scope of the case. Usually one analyst is assigned a case, but may ask others for help to get the results out faster.

Best scenario (which never happens), DNA could possibly be done on an exhibit as small as a knife in 48 hours. Then the report has to be reviewed by two other analysts before it can be sent to law enforcement. That’s not including a search of the FBI database if there are no suspects in the case. A manual search of the database may be done in rare cases, otherwise it’ll take another week to see if the DNA profile “hits” anyone in the database.

Most places don’t do blood typing anymore because it’s kind of time consuming and obviously not as unique as a DNA profile. The most that could be said in a preliminary report is to verify that the stain on the knife is, in fact, blood. It seems silly, but they do have to verify that it is blood and not cocktail sauce or something on the weapon.

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Amryn Cross is a full-time forensic scientist and author of romantic suspense novels. Her first novel, Learning to Die, will be released in September. In her spare time, she enjoys college football, reading, watching movies, and researching her next novel. You can connect with Amryn via her website, Twitter and Facebook.