Forensic Question: Solving Cold Cases

My question is about cold cases. Are you able to test for DNA from blood on a knife or clothes from 30-40 years old? Also, if the remains of a body were found in a mine shaft, could you tell the manner of death from that same time or even older, say, 150 years old? How would you do this and how long would it take? Thanks so much for your help!
Amryn Says:

Cold case investigations have come a long way with the use of DNA technology. Answers that would have been impossible 20 years ago are now commonplace. The problem with cold cases is often in the handling of the evidence. On the knife or clothes that you mentioned, when they were first collected from a crime scene 30-40 years ago, the investigator may not have worn gloves. That seems shocking given what we know now, but it wasn’t all that routine a few decades ago.

What that might mean for your DNA results is that you get a mixture—say, the victim’s blood and another unknown profile. Now, does that profile belong to the killer or just the detective or crime scene tech that handled the evidence without gloves? Without something to compare back to, you won’t be able to say.

Let’s assume best case scenario, though. If the bloody evidence was stored and handled properly, it is definitely possible to get a DNA profile from the blood present on a knife or on clothes. This can usually be done with routine DNA testing, which generally takes 2-3 weeks. Of course, for the purposes of fiction, the DNA could be “rushed” and then results would possibly be available as soon as 48 hours. This testing will probably be done at the police department’s or state’s crime lab.

As far as a body in a mine shaft, unless the body is frozen, it’s likely to be not much more than a skeleton by the time it’s found 30-40 years later, and certainly 150 years. However, if the manner of death was some sort of trauma (i.e. broken neck from a fall or stab wound where the knife grazes the bone), a lot can still be determined from bones.

In most cases, a forensic anthropologist would be the person to make that determination. Some states have one on staff while others call in an expert like Dr. Bass (founder of the Body Farm) when they are needed.  I would say the time frame for that sort of determination is at least a couple weeks, though I’m sure there are cases where it could be done faster. And I should also mention, many forensic anthropologists like to be present when the team is recovering the bones to make sure none are missed and to make observations based on the position of the bones.


Amryn Cross is a full-time forensic scientist and author of romantic suspense and mystery novels. Her first novel, Learning to Die, is available on Amazon. The first book in her latest series, loosely based on an updated Sherlock Holmes, is available for pre-order onAmazon. Look for Warzonein January 2015. You can connect with Amryn via her websiteTwitter and Facebook.

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.


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.