Expert: Robin Sexton - 5/25/2008

Question
Hello, Robin! I am working on a script involving the Miami Metro Police
Department and an investigation surrounding a killer who wets himself. But I
have several questions concerning urine found at crime scenes. (I apologize
in advance for any nausea this might cause.) 1.) If urine is detected at a crime
scene, what is the first assumption made? That the urine belongs to the
murder victim who possibly became incontinent out of terror or anxiety?
2.) Do murder victims sometimes lose control of their urine as their body
begins to shut down? 3.) How is the urine extracted from a crime site? 4.)
Who performs the urinalysis? 5.) What can a urinalysis uncover about the
person to whom it belongs? What substances are usually found in a urine
sample? Can such a sample ID the criminal if it in fact belongs to the
perpetrator? 6.) How do things change if the urine dries before police make it
to the crime scene? 7.) And lastly, how do things change if the urine mingles
with the blood of the victim (procedure-wise)? Does ID'ing the murderer
become more difficult/impossible? Thank you so much for putting up with
this.

Answer
Harmody,

I will have to start by saying that i am not an expert in Urine analysis or DNA extraction and processing. I know enough to know what to ask my experts for.  I have also had a lot of disappointment is not being able to get what i want.  First point is that assumptions should not be made at a crime scene, theories yes but not assumptions.   The biggest indicator of who left the urine would be on location.  Understanding the difference in male / female plumbing you would look at how high the urine may have been left.  If we are looking at just a puddle on the floor be hard to say who by that. Was it walked through? are there drips ? is the clothing urine stained or soaked ? What crime or crime, robbery, murder, sex crime ?  Was it part of the sex act or part of the suspects crime ?
2) Yes when people die the bladder will release, not all the time but enough.
3)  It is extracted or recovered like other fluids, either soaked up with a sterile medium, dissolved with distilled water. Carpet or some other material could be cut out and taken to the lab for further analysis.
4)  Urine analysis would be preformed several different ways. First factor is how much quantity are you dealing with.  The police crime lab would do the first analysis looking for DNA, if there is enough you may be able to do some drug screening.
5)  What are we looking for? first would be DNA.  Females expel more cells via their urine then males.  You would look for some drug indicators.  Lastly if there is a sufficient quantity and it was necessary a sample could be sent to a medical specialty lab for very specific tests, similar to what a medical doctor could look for.
&) How do things change ?  quickly, Urine air dry's fairly quickly unless absorbed in something.  Being exposed  to air and the environment contaminates it very quickly.  Urine is also fairly corrosive.
7)  Anytime you mix body fluids you have a serious problem.  The biggest problem is in mitochondria DNA where most labs want a non mixed sample for testing.

You have asked questions that require some very detailed and technical answers.  Sorry i couldn't provide better answers, Hoped i helped a little though

Robin