A crime scene can occur anywhere and at any time of the day: in a car, at a home, on a body of water, atop a mountain, in public places or private ones, and in the daytime or during the night. So the method chosen for searching a crime scene is basically determined by where---and when---the crime occurs. The popular methods used to search a crime scene include: grid, line, link, ray, spiral and zone.
Crime Scene Integrity
Crime scene investigators often only get one chance to properly search a crime scene before contamination (introduction of foreign materials) to the scene becomes an issue. As more and more people arrive at the scene---from the general public and news media to medical and law enforcement personnel---the scene's evidence loses its integrity (ability to be introduced as evidence into a court of law) for law enforcement purposes. That is one reason why the link method is the most common one used: it is less likely to contaminate the scene.
The purpose of searching a crime scene is to identify and secure evidence, enabling proper understanding of the events that occurred, as well as physical material to support possible arrest, prosecution and conviction. Therefore, the method employed (grid, line, link, ray, spiral or zone) will actually be chosen based on the type of crime that occurred, the crime scene location (and difficulty of access to it), as well as the resources and equipment capabilities available. So whichever method meets those criteria will be deemed the most popular for that crime scene at that time.
Most Popular Method
According to Henry Lee, recognized national forensics expert of the Connecticut State Police Forensics Crime Laboratory, the link method is the most common and popular way of searching a crime scene, and it is a very productive approach. This method seeks to link the victim, physical evidence, and the scene, to the suspect.
This particular method, however, requires much from an investigator: they must be very observant at the scene, able to discern the meaning of their findings, and capable of forming logical links between crime scene activity---and the likely places additional evidence could be found at the scene as a result. (See Henry Lee's book in the Resources section below.)
Link Method More Flexible
In addition to being the most common method used, the link method can to be used in conjunction with any of the other five crime scene search methods, because it involves observation, analysis, and deductive reasoning. However, the other methods--the grid, line, ray, spiral and zone--do not have this flexibility, since these five search methods rely solely on physically covering a geographical crime scene space by walking in a pattern of some sort (line, circle, grid or zone).
Method Ensures Integrity
In addition to being the most popular, practical, and flexible method, the link method has another attribute: it doesn't risk contamination of the crime scene. In the other methods, more than one individual usually walks the crime scene (in a straight line, grid-like, or circular pattern), potentially introducing foreign material into the scene and compromising potential evidence.
But the link method restricts physical interaction to areas of the scene that have already yielded obvious evidence (a dead body, a gun), and any area of interest generated due to observed clues (bloody prints on a window sill) or deductive reasoning (a shell casing is missing, and there is a hole in one of the walls).