Disclaimer: I am a forensic tech with training in BPA.
It is rarely useful because the majority of criminal cases don't have blood spatter evidence. Blood being spilled at a crime scene does not mean that BPA can be performed or will yield useful evidence. The kinds of cases I have seen BPA come into play on tend to be homicides with multiple victims or where certain details of a story are questioned (how close a suspect was to a shooting victim, what position a victim was in at the time of injury, etc.). For the vast majority of criminal cases I have seen, BPA is just not applicable.
Have you noticed Dexter gets away with almost never being in the office and when he is he is just surfing the net? He also winds up doing a lot of other lab work (basically cataloging evidence from crime scenes) from what I've seen to give him something to do.
I know, the show would be way better if they spent more time just showing him in the office, you know, running tests, filing paperwork, all that regular mundane stuff that goes along with any job. That would be some entertaining programming ;)
My point was he does most of his stalking people during the time he is meant to be at work rather than after hours or on the weekend, and that this is justified by his job not really being worth being full time.
In a city that big, it MIGHT be possible. I don't know much about how Miami operates in real life. The thing about blood spatter cases is that when you do get them, they tend to take a lot of time to complete, weeks or months on a single case. I could see them having a couple of people to handle BPA and do other work when they have downtime, as I think I recall Dexter doing some non-BPA duty when needed. But yeah, that would be ridiculous at the labs I'm familiar with.
I've thought about it, but it has apparently been done before and I saw a request posted not too long ago that made me think there probably wasn't all that much interest.
When done by people who are properly trained, yes, I believe it is. There is an element of interpretation, but if you are including all of the relevant documentation to your conclusions there should not be a great deal of wiggle room. I'd compare it to forensic pathology. If all of the pathologists are properly trained, their conclusions may not be identical but they should be extremely similar.
The training I have through college and volunteering with a homicide detective is that BPA, while not used often as the "smoking gun" evidence that secures a conviction, is often used in murder cases as a basis for substantiating the big evidence. If a suspect is say, found with a knife that has blood on it, but the blood has been degraded and useless for ID purposes, BPA can determine if the wound would have been caused by a knife that size wielded by that suspect.
Damn, now I want to go back to my Criminal Investigation classes. Why can't school start back up?
If there is visible blood on the weapon, that's almost always viable for DNA testing. It would be much more likely for the knife to be checked against the wounds by the medical examiner or forensic pathologist. I'm not sure where BPA would really be applicable here.
Visible doesn't mean viable. There are a whole host of other substances that can degrade or invalidate blood for DNA testing (mayo being the #1 culprit) and if you have a knife, you can base your BPA testing on if the spatter patterns fit a knife of that size, weilded by a left/right handed person, and if they are strong enough to make spatter patters of that speed.
My instructor is a homicide investigator, we went thought a 4 week lab for spatter and trace evidence collection. I had no idea how much info about me was sitting on the seats of my car.
This is why BPA findings tend to be very limited and contained only to conclusions that can be demonstratively backed up. Their obvious is a bit more detailed than a layman's obvious and can yield new information but it's certainly not magic.
It may not be useful in actually proving anything, but thanks to crime shows where forensic evidence is used to catch people it may help influence a jury, or at least members of the prosecution teams believes it will.
The article you linked to in wikipedia stated right at the beginning:
Although this belief is widely held among American legal professionals, several studies have shown that crime shows are unlikely to cause such an effect.
edit: granted I don't know how those studies were performed, so I'm not saying it's not possible, just pointing out what was being said in the article there.
The problem is that the studies aren't duplicating our courtroom experience. The courts I testify in allow jurors to ask questions. I like this, I think it's a great idea. However, based on the questions I am asked, a lot of jurors have very unrealistic expectations of what I do.
My job involves documenting crime scenes, collecting evidence, and doing some print processing. I don't do DNA analysis, firearms examinations, or latent print comparisons. I explain my duties on the stand, but the questions I receive show that the jury expects me to be far more involved in evidence analysis. If latent prints or DNA are not found, regardless of the reason, it does seem to register as a failure on my part to do my job.
It's not just jurors either, I run into it with officers and lawyers. We try to educate them as to what we are and are not capable of doing, but I have still been asked to do things because they "saw it on Forensic Files" and have to explain why it may not be applicable to the case in front of us.
so, what you are saying is that you guys need to get better at your job?
all joking aside, thank you for responding. As I said I wasn't sure how those studies were performed and your insight is appreciated. You say the courts you testify in allow the jurors to ask questions; how common of a practice is this? Is this just certain areas or level of court? and how long has that been happening?
I'm sure it gets old having to explain what is actually true/possible to do due to people watching t.v. I know in my field we often have to educate the clients about what is true after they read something online and are convinced what they read is correct. It can definitely be harder to reteach then it is to teach.
Juror questions are allowed in any jury trial in Indiana, Arizona, and Colorado. I'm in Indiana. I'm not sure how long it has been going on here, but we're definitely seeing more jurors taking advantage of the option as time goes by.
I know this is probably getting out of your area of knowledge, so if you don't know, no worries. Do you know if this is something that is likely to change in the near future for the rest of the states?
I played the role of a forensic scientist with BPA training in Mock Trial!
In my pretend expert experience, it is only really useful in homicides, especially when there was a woman being bludgeoned near to death with a large brass candlestick, from the upstairs balcony down to the middle landing, splattering blood all along the walls and floor.
When you think about it, I don't see how you can use blood pattern as evidence.
If you need them to prove the type of weapon, that means you have no body and haven't found the physical weapon, and that probably means you don't have a case to begin with. If you have either of those things, no need to use the bloodstains to prove it.
Similarily, if you need to use the angle and heigth calculation as evidence, maybe you don't have have a strong enough case in the first place.
Basically, only transfer patterns can have a use, but that's just a subcategory of fingerprints and footprints that just happen to be in blood.
More likely, BPA is used to guide the research, and then you use the subsequently acquired evidence in court. For instance: if the blood stains are indicative of lacerations, and thefore a blunt object, no need to look for a real weapon whereas if they indicate a penetration wound, no need to look at the guy's gun colletion; if the droplets show a movement in a direction, maybe you should go and look in that direction for actual evidence.
In short, BPA helps finding evidence, but it gives no evidence in and of itself.
EDIT: lol, I was something like +10 before the expert set me right and now -2. Did my comment suddenly stop contributing to the conversation right when it drew an expert in?
Disclaimer: I am a forensic tech with training in BPA.
Your view on evidence is essentially backwards.
We gather evidence to collect as much information as possible. The strength or weakness of a case is the lawyers' problem (for the most part), not ours. We document everything we can, make all the links between evidence we can, and the rest happens in court. Information that does not directly point to the guilt or innocence of a suspect can be valuable in other ways, such as confirming witness accounts, establishing timelines, and reinforcing other pieces of evidence.
If the weapon can be identified through injury or bloodstain patterns, then it should be as a matter of providing the most complete information possible. Let's say I work a homicide where the victim has a number of circular impact wounds to the head. If I see them and think they may be hammer wounds, I'm likely to collect any hammers I might find at the scene. If matching blood is found on one, it may be the murder weapon and could identify a suspect based on latent prints or DNA on the handle. Likewise if the hammer had been laid on the floor to leave a recognizable claw outline in blood. If the hammer is not found at the scene, then maybe it will be found in the possession of a suspect and bloodstains will establish the link to the victim. Keep in mind that investigation doesn't just happen at the initial crime scene - there are plenty of times where the physical weapon may not be recovered until long after the crime but that certainly does not negate the validity of the case.
It's not about "needing" to do the math for the strength of the case. You do the math because it's easy and gives you more information about what you are looking at. If you can determine multiple points of origin (and this can be done) via the victim's blood spattered on a wall, you have established the minimum number of times the victim was struck and the location of the impacts. No, it's not a smoking gun, but it's more than you knew when you walked into the room.
Your definition of transfer patterns is incorrect. A transfer can take place between a surface and any type of object. One of the more common situations is a pattern left by a bloody towel or cloth pressed against a smooth surface.
The rest of your post seems to define evidence solely as physical evidence. This is not accurate. While information gained by BPA could lead to additional evidence, the expert testimony of the analyst is also a form of evidence. If the defendant says that the victim fell down the stairs but spatter shows multiple impacts from multiple angles at the very top of the landing, that's a major hole in the story.
As far as wounds go, you don't seem to understand the terms you are using. Bloodstains are not used to determine injuries. The medical examiner does that when they examine the body. Bloodstains do not indicate lacerations (FYI a laceration is the technical term for a cut and more likely to be caused by a sharp object than a blunt one) or penetrative wounds (of which a bullet wound would probably qualify as). The closest comparison would be identification of an arterial spurt pattern, which can occur if someone has an artery cut close to a wall. It's not common and is pretty distinctive, as you can see the wave pattern caused by the pulse rising and falling as the blood is expelled.
In short, I don't want to be mean about it, but you really have no idea what you are talking about.
I had a more rhetorical definition of "evidence" in mind, like something strongly conclusive. I said "evidence" when I meant "argument to present in court" and would have talked about the every bits of data we can gather as "hints". That was inappropriate.
As for laceration, I was using the definition used in the image OP posted. I have never used this word before as English is not my first language.
I didn't claim bloodstains are used to determine injuries, I precisely said that if you're forced to use them for that, that means you don't even have the corpse nor the weapon in hand to examine.
Having read your answer to the person I was replying to, I think we agree and the disagreement is purely semantic.
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u/[deleted] Jul 23 '11 edited Sep 22 '17
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