The victim's shoulder is under a stone block in the dark. In daylight the stone block is not on his shoulder yet no one has moved it. Ducky has just arrived. Tim is taking initial photos.
Crimes occurring in a national park are in fact investigated by the US Park Police. There would not be a joint investigation as shown other than perhaps the FBI on a high-profile death such as was the case with White House employee Vincent Foster in 1993..
The mission of NCIS involves the security of the Navy and Marine Corps. They would not undertake an investigation involving the illegal selling of animal meat. However, since the bushmeat investigation stems from the murder of a Marine, NCIS is within its purview to follow the evidence wherever it leads, as long as the scope of it is kept to how it relates to the murder.
Gibbs threw a smoke grenade into the back of the van. It went off twice.