Building a case = an attempt to build up supporting evidence and discredit opposing evidence during the cross-examination of evidence (e.g., eye witnesses, forensic evidence, expert testimonies, etc.)
Making a case/argument = an attempt to persuade (by giving reasons) the jury or the judge of a particular verdict during the closing argument.
Attorneys have access to all evidence prior to the trial and therefore come to the court with some theories in their minds. Likewise, eye witnesses, law officers, forensic scientists, and other experts have their own theories as well. But the thing is: During the cross-examination, none of them are allowed to "make a case" for a particular verdict (i.e., explain why a certain verdict should be made).
"The attorneys for the defense and prosecution begin forming a case, witnesses are questioned, forensic scientists and criminologists help formulate theories."
If this sentence is describing the pretrial process, "forming a case" cannot mean "making arguments" because at that point there is no audience (i.e., the jury or the judge). By the way, the attorneys are prohibited to formulate theories with the witnesses. That's called witness contamination and is against the law. There are certain regulations regarding what a prosecutor can ask and say during a pretrial witness interview.
If this sentence is describing the process during the trial, "forensic scientists and criminologists help formulate theories" means "the testimonies given by forensic scientists and criminologists help the jury or the judge formulate theories in their minds."