Responses apa 7 50-100 words 1 reference POST 1: Biological Evidence – Semen Semen that is found at a crime scene can be collected, examined, and prese

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Responses apa 7

50-100 words

1 reference POST 1: Biological Evidence

– Semen

Semen that is found at a crime scene can be collected, examined, and presented at the criminal trial as direct or circumstantial evidence for a sexual assault case. The semen can be used to place a potential suspect at the crime scene, but some factors can discredit semen being found. For example, if the victim can recall the perpetrator or anything from the incident and if the potential has a strong alibi that can place the individual somewhere else during the crime.

CDS evidence

– Crack cocaine

Crack cocaine samples are determined through presumptive and confirmatory testing to confirm the chemical compounds and to identify exactly what the drug is. Crack cocaine can be used in a criminal trial when an individual car is being towed and the law of the state and department states that an officer should search the vehicle before it is towed and used as direct evidence. This evidence could be discredited if, during the time of the interaction of the individual and officer, there is a violation of their Fourth Amendment.

Blood pattern evidence

– Void Stains

Void stains can be used in a manner to prove that during a crime there was an object or person present at the time of where the crime happened due to a bloodstain pattern. Void stains can prove to analysts that there is something so that it can be replaced to show what happened during the time of the crime. Bloodstain patterns can be used as direct and demonstrative evidence. Void stains can be discredited if the forensic analysts cannot sufficiently testify to jurors to prove that they are an expert at their job and explain thoroughly what happened at a crime scene. If an expert witness is unable to properly testify to their findings it can cause conflict during the trial and discredit anything about the void stains, especially during cross-examination.

DNA evidence

– Hair

Hair fibers would be presented in a criminal trial to prove that as circumstantial evidence to support the idea that a suspect was at some point at the crime scene, or the hair has similar traits to the suspect. Challenges that can be posed from hair fibers are that the fibers could be old or that the fibers could come from another person thought it may be like the defendant. If the defendant can have direct evidence to prove that they were not there at the scene it could discredit this type of evidence.

Document evidence

– Printed Document

Document evidence can be used in a manner of direct evidence in a trial to prove that document was printed by an individual based on toners, character shapes, or tool marks that could be on the documents from the printer belts, rollers, and gears (Pontzer, 2020. If proper samples are collected and presented in court it can then link a defendant to a crime or establish that document was formed by an individual. Document evidence can be discredited if the most recent writing samples are not comparable to the evidence and if an eyewitness testimony is contradicted at any point during the criminal trial.


Gerbis, S. (2020, October 15). How bloodstain pattern analysis works. Retrieved November 21, 2021, from

Houck, M. M., & Siegel, J. A. (2015). Fundamentals of Forensic Science: Vol. Third edition. Academic Press.

Houck, M.M., & Siegel, J.A. (2015) Part 4 Chapter 13 Illicit drugs. Fundamentals of Forensic Science. (pp 315-352). A Butterworth-Heinemann Title.

Pontzer, D. (2020). Document examination in criminal investigations. Salem Press Encyclopedia of Science.

Circumstantial vs. Direct Evidence in Wisconsin Criminal Cases. (2018, August 10). Retrieved from,

Serology. Bureau of Criminal Apprehension. Learn more about DPS, Divisions, Programs, Boards and Committees. (n.d.). Retrieved from,


Before the advent of DNA analysis, serology was the best way of identifying the perpetrator of a crime. In sexual assault cases it was especially important to retrieve genetic material from the victim with the hope of being able to make an arrest. During a court case, the evidence would be presented as real evidence, a physical piece of evidence that is helpful in connecting a suspect to a crime. Real evidence also can enlighten investigators on the timeline of the event with things like fibers, weapons, blood, or semen, for example (Houck & Siegel, 2015). An expert in serology would be the one to testify on the tests that were performed and their findings from those tests. Serology is not as accurate as DNA, and it is possible for a victim’s genetic markers to overwhelm those of the assailant’s, especially if there is a very small amount of material available for testing (Garett & Neufeld, 2009). Serology can, however, “exclude individuals or place individuals within a percentage of the population that possesses a given type and cannot be excluded as a source of the fluid (Garrett & Neufeld, 2009).” Misstatements of the statistics regarding the population to make the tests seem more like the defendant is guilty can be used to discredit this defense (Garret & Neufeld, 2009).

DNA evidence has been touted as the gold standard for evidence in forensic science (Dror & Hampikian, 2011). In court, a DNA expert would interpret the findings from any tests they ran of the evidence to help the jury understand the ramifications of the evidence. Since the actual evidence itself would not physically be in court, any reports from the lab would be considered demonstrative evidence, which does not directly come from the crime scene but is developed by study of the crime scene (Houck & Siegel, 2015). However, there is potential contextual bias where DNA evidence is concerned. If an analyst has some of idea of the crime or what the detective thinks happened, there may be some unintentional bias on the part of the analyst. Different experts could arrive at disparate conclusions even given identical evidence (Dror & Hampikian, 2011). DNA is a complex science that requires human examiners “making a variety of subjective judgements that are susceptible to bias (Dror & Hampikian, 2011).” This is particularly true when dealing with complicated situations, like mixtures of DNA. It is also possible for cross contamination to happen anywhere in the chain of custody from collection to the lab, and the defense could potentially use that against the prosecution. Primary and secondary transfers are possible, and according to Cale et al. (2016), forensic analysts should be careful of both, as they could lead to falsely connecting someone to a crime scene, foreign DNA could be introduced into a DNA sample, and it could have analysts concluding that DNA left on an object is only possible from direct contact. However, Locard’s Exchange Principle also works with an intermediary, so it is possible for someone with no link to the crime scene to have their DNA found there (Cale et al., 2016).

Blood pattern analysis has been in use since the 1800s (Laber et al., 2014). Since it is so often found at crime scenes, looking at the patterns can be a clue as to what happened during the incident. In court, it would be presented as demonstrative evidence, likely photos and/or sketches of the crime scene. A blood pattern expert would discuss the evidence with the jury and lead them through their interpretation of what happened. There are a few ways that this evidence could be discredited, however. First, there may only be a small stain or only a few stains, which may or may not be enough for appropriate analysis (Laber et al., 2014). Where the blood landed can add complications; stains on a smooth surface will look different than stains on carpet or clothing (Laber et al., 2014). Analysts may also be given information particular to the specific case, like medical information or case circumstances which, according to Laber et al. (2014), can lead to bias on the part of the analyst. Blood stain analysts are also working against their methodology: like with fingerprint or other impression evidence, blood stain interpretation is really only done through experience of instructors and detectives (Laber et al., 2014). That lack of scientific backing could be a liability in the eyes of the jury.

Questioned document analysis is important in many cases. One that is not thought of often is organized crime, but De Alcaraz-Fossoul and Roberts (2017) explain why it’s a topic to explore. Activities of organized crime groups are usually undetected and uncontrolled by authorities, but their unique types of forgery used by each particular crime group can be used to identify that criminal network. They have to move their members, victims, and products between different countries so they need to forge legal identification like driver’s licenses and passports. These documents would be presented in court as real evidence and a questioned document specialist would explain to the jury how they came to their conclusions about what was forged. In this case, a few questions could be raised about the credibility of the evidence. The evidence submitted might not be the original document, and copies do not have as much information as the original to be examined (, n.d.). Document examiners can only compare like to like: if a standard is not available for comparison, the examination can not happen (, n.d.). Also, the examiner is not able to determine if counterfeiting happened if they only have a photocopy to look at (, n.d.).

More than a million people are arrested on drug charges each year in the US (Gabrielson & Sanders, 2016). Field tests, which are presumptive, not confirmatory, are often used by police officers at the scene to confirm presence of controlled dangerous substances (CDS) to either secure an arrest or let the suspect go. These tests, which have not changed much since their inception in 1973, are unreliable at best (Gabrielson & Sanders, 2016). According to the New York Times Magazine article by Gabrielson and Sanders (2016), some tests use cobalt thiocyanate to detect the presence of cocaine: the chemical inside the vial will turn blue if cocaine is detected. However, this test also tests positive for at least 80 other compounds, to include methadone, some acne medications, and household products. Also, hot weather can speed up the reaction or it can cause the test to have no reaction at all. In court, drug evidence would be presented as real or demonstrative evidence, depending on the amount of the drug present at the scene. Sometimes there is too little to be tested, and yet people still plead guilty to drug possession after seeing the field test done (Gabrielson & Sanders, 2016). If there is an extremely large amount of evidence, sampling will take place in lieu of testing each and every crumb of substance seized (Houck & Siegel, 2015).


A simplified guide to forensic document examination. (n.d.). Retrieved from

Cale, C. M., Earll, M. E., Latham, K. E., & Bush, G. L. (2016). Could secondary DNA transfer falsely place someone at the scene of a crime? Journal of Forensic Sciences, 61(1), 196–203.

De Alcaraz-Fossoul, J., & Roberts, K. A. (2017). Forensic intelligence applied to questioned document analysis: A model and its application against organized crime. Science & Justice, 57(4), 314–320.

Dror, I. E., & Hampikian, G. (2011). Subjectivity and bias in forensic DNA mixture interpretation. Science & Justice, 51(4), 204–208.

Gabrielson, R. & Sanders, T. (2016). How a $2 roadside drug test sends innocent people to jail. The New York Times Magazine. Retrieved from

Garrett, B. & Neufeld, P. (2009). Invalid forensic science testimony and wrongful convictions. Virginia Law Review 95(1)

Houck, M. M., & Siegel, J. A. (2015). Fundamentals of Forensic Science: Vol. Third edition. Academic Press.

Laber, T., Kish, P., Taylor, M., Owens, G., Osborne, N., & Curran, J. (2014). Reliability assessment of current methods in bloodstain pattern analysis. Retrieved from

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