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In the Federal Government, there are agencies that employ criminal investigators to collect and provide information to the United States Attorneys in the respective district.
You may already know some of the agencies, such as:
- Federal Bureau of Investigation (FBI)
- Drug Enforcement Administration (DEA)
- Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF)
- United States Secret Service (USSS)
- Homeland Security Investigation (DHS/HSI)
The investigators at these agencies investigate the crime and obtain evidence, and help prosecutors understand the details of the case. The prosecutor may work with just one agency but, many times, several investigating agencies are involved.
Part of the investigation may involve a search warrant. The Fourth Amendment of the Constitution usually requires that police officers have probable cause before they search a person’s home, their clothing, car, or other property. Searches usually require a search warrant, issued by a “neutral and detached” judge. Arrests also require probable cause and often occur after police have gotten an arrest warrant from a judge.
Depending on the specific facts of the case, the first step may actually be an arrest. If police have probable cause to arrest a suspect (as is the case if they actually witnessed the suspect commit a crime), they will go ahead and make an arrest.
A prosecutor evaluates a case, and uses all the statements and information they have to determine if the government should present the case to the Federal Grand Jury — one in which all the facts lead to a specific person or persons who committed the crime. However, before the prosecutor made that conclusion, they have to look at both direct and circumstantial evidence. Direct evidence is evidence that supports a fact without an inference. Testimony of an eyewitness to a crime would be considered direct evidence because the person actually saw the crime. Testimony related to something that happened before or after the crime would be considered circumstantial.
The second type of evidence is circumstantial evidence — statement(s) or information obtained indirectly or not based on first-hand experience by a person. Circumstantial evidence includes people’s impressions about an event that happened which they didn’t see. For example, if you went to bed at night and there was no snow on the ground but you awoke to snow, while you didn’t actually see it snowing, you assume that it snowed while you slept.