Nichols tells Stevens that in a military court it is very difficult to make a murder case when there is no body. This is true, but it is also the same in civilian courts. One of the main prima facie requirements for the prosecution in a murder case is that they have to show that someone is actually dead and without a body that can be very hard to prove, so the prosecution's job is twice as hard in these cases. In a typical murder trial the prosecution has to prove beyond a reasonable doubt the defendant intentionally killed the victim, which is often hard enough on its own. But in a murder trial where there is no body the prosecution also has to prove beyond a reasonable doubt that someone was actually killed, and without any evidence like a substantial amount of blood at the crime scene it is nearly impossible.
UCMJ stands for Uniform Code of Military Justice, which is the foundation for military law in the United States. It is a code of conduct for members of the United States military and it also outlines the military judicial system which is used to punish members of the United States military who violate the code of conduct. It closely follows the federal civilian justice system, with many of the same laws though military trials are often more swift than civilian ones and hand out harsher punishments since members of the military are expected to hold themselves to a higher standard of conduct. Although the UCMJ is stricter than civilian justice systems they are often ahead of the civilian justice system when it comes to making changes, an example being the UCMJ adopted its own version of the Miranda warning (a requirement for law enforcement to inform a suspect of their rights when being questioned and arrested) 15 years before civilian law enforcement agencies were required by the United States Supreme Court to use what became known as the "Miranda warning".
The squad cars and CSU vehicles at the cul-de-sac crime scene were from the 27th precinct, which is the precinct where Law & Order (1990) is set.