Evidence Presentation - Types of Evidence
Testimony that is corroborated by a separate witness can certainly strengthen a case for either the prosecution or the defense but in the case of a codefendant testifying for the defense, a third party verifying this testimony would be helpful in showing that their testimony is valid.
An expert witness is a person who is accepted by the court as a specialist on a specific area of expertise who has an understanding above and beyond that known or available to a typical individual. An expert witness's qualifications and experience as well as their background should be explained to the jury. A general idea of the witness's specialty as well as the length of time they've been considered an expert in their field should be provided to the jury and entered into the record to assure their credibility.
An expert witness's testimony for the defense can be conflicting to another expert witness's testimony for the prosecution and vice versa. As is the case with all testimony given at trial jurors must judge the testimony of each expert witness and make their assumptions about which one of them they believe, and on what the jury member feels to be the personal credibility between the conflicting expert witnesses based on their responses.
Cross-examination is the method of trying to uncover the truth by adversary attorneys through the analysis of the disputed so-called facts stated by a witness who has already testified. Each attorney questions the witness in turn, and each is allowed to requisition the witness on subjects disclosed by subsequent questions. A successful cross-examination will annul the testimony of the witness when they were originally questioned by the opposition.
Physical Evidence is evidence collected at the crime scene or evidence that is uncovered during a further investigation of the crime, the scene and surrounding area. Some examples of physical evidence are: a weapon used in the alleged commission of the crime, human hair, blood samples clothing fibers, fingerprints, DNA and other forensic findings, drugs and drug paraphernalia, shell casings, audio and videotapes and notes found near a victim's body just to name a few. Proof of a proper chain of custody is required for all the items mentioned as examples to be included as accepted evidence and not be excluded by the judge.
The chain of custody is the movements and locality of any physical evidence from the moment it is obtained from the alleged crime scene or other areas associated to the alleged crime as well as items recovered during a subsequent investigation up to the time it's offered at trial. Documentation must confirm that the evidence was not substituted, tampered with, or contaminated. Law enforcement may also have to prove to a judge that they secured and protected a crime scene, that the evidence retrieved is authentic and genuine, identify an item by serial number if there is one and that it has a connection to the case as well as identifying an object by observations and personal knowledge. They may also have to testify as to where the object was procured and the method used in obtaining it.
The chain of custody requires that all law enforcement officers as well as medical personnel and other intermediaries that had possession of the evidence and handled it must appear as witnesses to testify that the specific evidence had not been tampered with, substituted or contaminated while each witness had custody and control of the evidence to show reasonable probability that the evidence was not altered, damaged or replaced.
Evidence that breaks the chain of custody can be excluded by a judge from ever being presented at trial.
As opposed to a civil trial, rules for admissibility of evidence are much more stringent for evidence in a criminal case due to the constitutional protections a defendant is entitled to under the Constitution. The final results of a vast number of criminal cases have more than likely been decided by the judge's decisions and rulings on which evidence is admissible and which is excluded. As an example, if a judge believes a confession or an alleged murder weapon was obtained improperly he may exclude it, resulting in an outcome that may have been contrary if the exclusions didn't occur.
Circumstantial evidence is incidental evidence that suggests the presence of a leading fact in question, but doesn't by itself substantiate it, although the appearance of this evidence tends to be conclusive and appear to be damning, it won't necessarily contribute to a guilty verdict. Circumstantial evidence can be a fingerprint; but if the defendant had reason to be at the crime scene at a separate time other than when the crime occurred the fingerprint can be considered circumstantial. The same could be assessed for other DNA evidence.
Obtaining Physical Evidence from a crime scene
Another act that can disqualify a physical item from reaching trial is an unlawful search by law enforcement. Private premises such as an apartment, a home, or office cannot be entered by police without consent or with a legally obtained warrant unless exigent or emergency circumstances exist. Click here for a full explanation located in the sixth paragraph on the page dealing with arrest.
At a crime scene where a serious crime has occurred law enforcement can make a swift warrantless search of the area and its surroundings to determine if there are additional victims of the crime they've been called to investigate as well as checking to see if a perpetrator is still at the scene. Additionally, during the progression of legitimate emergency activities at the crime scene officers can seize evidence which is in plain view. Evidence found when police are responding to an emergency may be used in criminal trials. However, officers can only stay at a crime scene for the purpose of searching it without a warrant for what is considered a reasonable period of time.
Obtaining evidence in emergency aid situations
If police observe an individual that appears to be injured, unconscious, or possibly deceased when looking through the window of a dwelling or an open door to the residence, they can search the premises and evidence found at the scene may be presented. Police can also stop and search vehicles where shots have been fired. Additionally, after a pursuit of a vehicle that has come to a stop, officers are under no obligation to delay a search if the failure to an immediate search could gravely endanger them while looking for weapons.