In most countries detectives may obtain their position by competitive examination covering such subjects as principles, practices and procedures of investigation; interviewing and interrogation; criminal law and procedures; applicable law governing arrests, search and seizures, warrants and evidence; police department records and reports; principles, practices and objectives of courtroom testimony; and police department methods and procedures.
Detective Police, also called Investigations Police (USA) are responsible for investigations and detective work. Detectives are plainclothes investigators who gather facts and collect evidence for criminal cases. They conduct interviews, examine records, observe the activities of suspects, and participate in arrests.
Mass media have done much to create a romanticized version of the detective. Their counterparts do exists in real life but the modern detective may easily be someone who sits at a computer screening lots of methods used in commission of a crime or who tests samples for DNA identification. Most detectives are trained in modern investigative techniques and in the laws of evidence and criminal procedure. They spend most of their time on paperwork and hours of interviewing.
Most police investigations begin at the scene of a crime. There are some types of evidence that is located and recovered at a scene: 1) Impression evidence includes fingerprints, tool marks, footwear, fabric impressions, tire marks and bite marks. 2) Biological evidence includes blood, body fluids, hair, nail. 3) Trace evidence includes paint, glass and fibres. 4) Firearms include weapons, gun powder patterns, casings, projectiles, and cartridges. Experts are particularly adept in the microscopic examination of spent bullets and cartridge cases.
The use of DNA profiling is regarded as reliable asfingerprintingto check the unique characteristics of an individual. Fingerprints (also includes palm prints and bare footprints) are the best evidence to place an individual at the scene of a crime. The identifying fingerprint pattern dusted with powder could be seen and photographed or digitally recorded. By comparing fingerprints at the scene of a crime with the fingerprint record of suspected persons, absolute proof of the presence or identity of a person can be established.
If using the method of DNA analysis, then blood can be matched back to an individual with a high degree of probability. DNA profiling can positively identify an individual from a specimen of blood, hair roots etc.
In the Scientific community the crime scene investigator is accepted as a forensic specialist. His specialty is considered a professional organized step by step approach to the processing of a crime scene. Extensive study, training, and experience in crime scene investigations are needed for the investigator to be proficient in the field. He must be a specialist in all areas of recognition, documentation and recovery of physical evidence that may be deposited at the scene.