Synonyms for probable:

feasible

plausible

possible

По-немецки, möglich в одном из самых первых значений как раз и будет "possible"

И этот ваш "probable cause" - ничто иное, как "возможная причина (загреметь в каталажку)".

Ну и вести с полей... со страниц журналов типа USA Police.com и тому подобного:

"There is a difference between what is required to prove guilt in a criminal case and what is required to show probable cause for arrest and search." (Brinegar v. U.S.)

"Innocence of the charge is largely irrelevant to [the question of the existence of probable cause]. The Constitution does not guarantee that only the guilty will be arrested." (Baker v. McCollum)

Probable cause is much less than proof "beyond a reasonable doubt," which is the much higher standard the prosecutor must meet in order to convict a defendant.

Probable cause is much less than "clear and convincing" proof, which is the higher standard that must be met as to certain legal rulings, such as whether jury challenges were improperly based on group bias.

Probable cause is less than a "preponderance of the evidence" (meaning 50 percent-plus), which is the plaintiff's burden of proof to win a civil case.