"4.5.3 Expert Opinions. Many courts have set a threshold of
certainty for the investigator to be able to render opinions in
court, such as “proven to an acceptable level of certainty,” “a
reasonable degree of scientific and engineering certainty,” or
“reasonable degree of certainty within my profession.” While
these terms of art may be important for the specific jurisdiction
or court in which they apply, defining these terms in those
contexts is beyond the scope of this document."

The courts use the definition of probable as "more likely than not." 50-50 is not "more likely than not." >50% is. This has always been the case, though I can only speak with experience for the last 53 years.

Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[www.kennedy-fire.com]