The Detectives take control and responsibility for Evidence once it has been relinquished from the SOCO team so that this information can be used by the Detectives in order to form a case against the person they are investigating. The detectives are also in charge of interviewing witnesses and interrogating suspects in order to gain more information about the crime and to hopefully gain a confession.
Another job of the Detectives is to inform the SOCO team which evidence they believe is pertinent to the case, and whether specific photographs, measurements or collections are needed.
Many CID will be at least to some level trained Forensically in the correct way to collect evidence, and how to handle samples, meaning that it is often for Detectives to also collect evidence themselves from a crime scene, and then sighing for it in the exhibits log.
Once the a case they have been working on is ready to go to court, it is the role of a Detective to write an in depth report, detailing all of the crimes, evidence and conclusions which led them to an arrest, it is their responsibility therefore to take notes throughout the entirety of the investigation in order to maintain an accurate and precise report for the courtroom.
The OJ Simpson Case
In the OJ Simpson case, the lead detective was Mark Furhman, a man who later turned out to be extremely racist. While at the crime scene, Furhman was seen stepping in the blood of the victims, therefore contaminating the scene, he then left footwear marks at the scene, therefore removing any possibility of determine who had been at the scene based on footwear marks left at the scene. He also allowed the SOCO team to do their job poorly, as he not only did not ask for any specific evidence, but he did not supervise them at all.
Furhman then continued to enter the property of OJ Simpson without obtaining a Search Warrant from a Judge, therefore leading all evidence found at the scene into question, especially due to his racist ties.
Finally, though taking notes at the crime scene neglected to pass the information he had found onto his successor as lead CID, therefore meaning that crucial evidence which Furhman had taken note of went un-collected, evidence which could have lead to a conviction.