A couple of SCOTUS decisions bearing on this are Texas v. Brown, 460 U.S. 730 and Illinois v. Gates, 462 U.S. 213, where the courts took pains to deny that "probable cause" is related to a number. From Texas v. Brown,
the Court frequently has remarked, probable cause is a flexible,
common-sense standard. It merely required that the facts available to
the officer would "warrant a man of reasonable caution in the belief,"
Carroll v. United States, 267 U. S. 132, 267 U. S. 162 (1925), that
certain items may be contraband or stolen property or useful as
evidence of a crime; it does not demand any showing that such a belief
be correct, or more likely true than false. A "practical,
nontechnical" probability that incriminating evidence is involved is
all that is required. Brinegar v. United States, 338 U. S. 160
From Illinois v. Gates,
The task of the issuing magistrate is simply to make a practical,
common sense decision whether, given all the circumstances set forth
in the affidavit before him, there is a fair probability that
contraband or evidence of a crime will be found in a particular place.
And the duty of a reviewing court is simply to ensure that the
magistrate had a substantial basis for concluding that probable cause
The question is framed in terms of probability that a certain individual is guilty, but that is not the basis for issuing a search warrant. Rather, a warrant may be issued if there is a fair probability that evidence bearing on a crime will be found. That would include evidence that exonerates a person (the system is not set up to only favor convictions). It would be highly impractical to assign a numeric value to probability of finding evidence, since there is more to the matter than just declaring "It must have been one of these three people".