In the New York City Police Department, rarely do the initial responding detectives collect, process, or analyze evidence in sexual assaults, major investigations, or homicides. Whether it is photographs, fingerprints, ballistics, or serology, the evidence is best left up to other detectives who are trained for these very specific forensic assignments. The NYPD's Crime Scene Unit (CSU) is an elite team of forensic detectives who form the backbone of a homicide investigation.
       An integral part of the Detective Bureau's Forensic Investigations Division, the Crime Scene Unit assists investigating detectives in all homicides, most sexual assaults and any other investigation their expertise is desired. The Crime Scene Unit has at the unit's disposal the necessary tools required to apply their expertise. They have the tools and equipment required to follow aq multitude of tasks including the trajectory of bullets fired, "lifting" fingerprints, cast tire impressions, forensic biology including blood, semen or other body fluids, hair, nail scrapings or blood stain patterns. The NYPD's Crime Scene Unit is not only prepared to process a "simple" crime scene, they are prepared to process a crime scene of catastrophic proportion as demonstrated when the unit processed the 1991 bombing at the World Trade Center.
      When the Precinct Detective Squad responds to a homicide, after ensuring that the basic procedures for safeguarding the crime scene have been implemented, the squad will analyze what they apparently have at hand. Among the numerous notifications they will make there after, one will be to the Crime Scene Unit. The Crime Scene Unit's dispatcher will ask appropriate questions that will determine how many detectives and what equipment to dispatch to the crime scene. Upon CSU's arrival, a team has been forged between investigating detectives and forensic detectives that will launch the investigation from the crime scene.
 
 

 Luminol

   A female is found fatally stabbed multiple times and buried under a pile of clothing in a closet in her Washington Heights apartment. During initial response and a canvass of the building, detectives from the 33rd Detective Squad receive information and immediately focused on the victim's paroled boyfriend who lived next door. The apartment's entrances are separated by about 5 feet of a mosaic-tiled floor.

    When the detectives visit the boyfriend's residence he is found in the apartment with several members of his family. The boyfriend denies being with the victim that day and also denies any knowledge or involvement in her slaying. Family members  provide an alibi that he had not been out of the apartment all day.

    Detectives notice that the boyfriend is wearing extremely clean, yet old beat up sneakers and also find out that he did a wash early that day. Also noted is a very clean floor between apartments. Detectives from the NYPD's Crime Scene Unit are called and after being conferred with, apply luminol to the unusually clean mosaic tiled hallway floor. Presto! Between the victim and boyfriend's apartments glow bloody sneaker prints that travel one way.... from the victim to the boyfriend's apartment. Suspect taken to the 33rd Precinct, sneakers confiscated, and detectives do a beeline to the medical examiner's office with the sneakers in  hand (but properly packaged to avoid cross-contamination). The victim's blood is found on the sneakers and a subsequent conviction for the murder of  is obtained.

       Luminol is a complex chemical cocktail that reacts to the iron
found in the hemoglobin of blood. Long after blood is cleaned up by a perpetrator at a crime scene, if not cleaned properly Luminol will speak on behalf of the victim

  DNA

    An elderly couple is found bludgeoned and stabbed to death in their apartment in a Washington Heights senior citizen's home. It was a gruesome crime scene that required an extensive blood splatter analysis by the New York City's Medical Examiner's Office and a tedious processing by the NYPD's Crime Scene Unit. The assailant left a pair of sox on the toilet in the apartment's only bathroom in what appeared to be an attempt to clean the blood off. The bright yellow sox with dark red stains had become the focal point for detectives from the NYPD and the now defunct New York City Housing Police.

    After an exhaustive investigation and the elimination of other possible suspects, the couple's paroled grandnephew became the prime suspect. Although employed with a local TV station as a graphic arts designer, the grandnephew had a severe cocaine addiction unknown to family and employer, and many thought the detectives had unfairly targeted him. To the detectives, lacking any other evidence, the sox became ever so crucial. Armed with the knowledge that fabrics often trap hair follicles and that the human skin sheds (we shed 1.5 million skin cells every hour), the sox were sent to the Medical Examiner's Office in an attempt to extract DNA. After several weeks DNA had been extracted.

    A warrant was obtained by homicide detectives and New York State Parole contacted. The paroled grandnephew, under the order of his parole officer, submitted a urine sample one early morning and the sample was sent to the Medical Examiner's Office. The grandnephew was told that it had to be his first urine of the day. If the urine is the first of the day, enough matter may accumulate overnight in the urethra to extract DNA. There was enough matter and DNA was extracted from the matter contained in his urine! A comparison of this DNA and that of the sox obtained earlier were a match.

   When confronted with the fact that the sox left at the crime scene, that bore traces of the victims' blood and were scientifically matched with DNA to him, the grandnephew immediately confessed to the double murder. He was convicted and sentenced to 50 years to life.

    It was one of New York City's first homicides solved with the use of what was then "new" DNA technology.