With the advent of DNA analysis and its subsequent admissibility in court, police officers have been able to identify with near perfect reliability who committed a particular crime. DNA analysis requires only a small sample, the technology can be used on samples that are too old for other types of testing, results from one lab can be checked against results from another lab, and results are easy to computerize. Nonetheless, DNA analysis is more time- consuming and expensive than conventional serological techniques and forensic serologists require extensive training in the use of DNA technology before they can be considered expert witnesses. Crime scene investigation involves the collection and processing of several types of evidence, including fingerprints, photographs, tool marks, bite marks, firearms, semen, glass, hairs and fibers, fingernails, impressions and casts, and documents. Evidence should be collected carefully so that it is not damaged, altered, or destroyed. Law enforcement can also use computers to assist in evidence processing, records management, fingerprint classification, and communications. Protecting the crime scene and accurately gathering or interpreting evidence may be the most important aspects of an investigator's job.