Police: Criminal Investigations

Criminal investigations can be either reactive, where the police respond to a crime that has already occurred, or proactive, where the investigation may go on before and during the commission of the offense.

The reactive criminal investigation process can be organized into several stages. The first stage is initial discovery and response. Of course, before the criminal investigation process can begin, the police must discover that a crime occurred or the victim (or witness) must realize that a crime occurred and notify the police. In the vast majority of cases it is the victim that first realizes a crime occurred and notifies the police. Then, most often, a patrol officer is dispatched to the crime scene or the location of the victim.

The second stage, the initial investigation, consists of the immediate post-crime activities of the patrol officer who arrives at the crime scene. The tasks of the patrol officer during the initial investigation are to arrest the culprit (if known and present), locate and interview witnesses, and collect and preserve other evidence.

If the perpetrator is not arrested during the initial investigation, then the case may be selected for a follow-up investigation, the third stage of the reactive investigation process. The follow-up investigation consists of additional investigative activities performed on a case, and these activities are usually performed by a detective. The process of deciding which cases should receive additional investigative effort is referred to as case screening. This decision is most often made by a detective supervisor and is most often guided by consideration of the seriousness of the crime (e.g., the amount of property loss or injury to the victim) and solvability factors (key pieces of crime-related information that, if present, enhance the probability of an arrest being made) (Brandl; Brandl and Frank).

Finally, at any time in the process the case may be closed and investigative activities terminated (e.g., victim cancels the investigation, the crime is unfounded, there are no more leads available, or an arrest is made). If an arrest is made, or an arrest warrant is issued, primary responsibility for the case typically shifts to the prosecutor's office. The detective then assists the prosecutor in preparing the case for further processing.

With regard to proactive criminal investigations, undercover investigations are of most significance (Marx). Perhaps the most well-known type of undercover strategy is the sting or buy-bust strategy that usually involves a police officer posing as someone who wishes to buy some illicit goods (e.g., sex, drugs). Once a seller is identified and the particulars of the illicit transaction are determined, police officers waiting nearby can execute an arrest. Another common strategy involves undercover police officers acting as decoys where the attempt is to attract street crime by presenting an opportunity to an offender to commit such crime (e.g., a police officer poses as a stranded motorist in a high crime area; when a robbery attempt is made, nearby officers can make an arrest). Undercover strategies are controversial primarily because of the possibility of entrapment. Although a multitude of court cases have dealt with this issue, the basic rule is that the police can provide the opportunity or can encourage the offender to act but cannot compel the behavior—a fine line indeed.