Challenges that are faced when examining controlled dangerous substance (CDS)

Discuss the challenges that are faced when examining controlled dangerous substance (CDS) evidence, bloodstain patterns, and DNA evidence.
Discuss a minimum of two ways in which the challenges mentioned above can be minimized or overcome.
Which of the above (i.e., CDS evidence, bloodstain patterns, DNA) presents the most difficulty in the collection of evidence and why?
Discuss the impact that each of the above (i.e., CDS evidence, bloodstain patterns, and DNA) has in establishing direct, circumstantial, and demonstrative evidence in a court case.