ἡ γὰρ ἀλήθεια καὶ τὰ πεπραγμέν᾽ αὐτὰ βοᾷ
For the truth and the facts speak for themselves.
The predicate agrees in person and number with the subject (which is its most salient complement). In the case of a subject in the neuter plural, however, the predicate is usually in the singular.
Plural, neuter subjects agree with a singular predicate for historical reasons. The ending of the neuter plural, in Greek -α