The crime scene is documented with written descriptions, photographs, video and sketches

Once the crime scene has been secured, investigators begin the second part of the process. The first step is determining the size and boundaries of the scene.
 
Entry and exit points are the first places to be checked. These are places where the criminal is known to have been and are therefore most likely to present clues.

Detectives then carefully move around the scene to try and establish exactly what happened and where. The crime scene is documented with written descriptions, photographs, video and sketches. 

Investigators first target the areas where contact is most probable – doorways or windows where the suspect may have entered or exited; or cupboards, drawers, safes and other storage places - particularly in cases of robbery.

Regardless of the extent of the crime scene it’s imperative that investigators make a thorough search within the boundaries. The CSIs systematically scour the crime scene searching for information. They criss-cross the location in a grid pattern, spiral or make linear sweeps the way a farmer ploughs a field.

The initial job is to concentrate on physical evidence that backs up the detectives initial theories. For example, toolmarks left from a forced entry, footprints left by an intruder, or indeed, blood stains or spatters. Anything, in fact, that helps detectives reconstruct the events that have taken place.