Acts 24:9

And the Jews also joined in the charge, affirming that these things were so.

Of course, the very presence of the high priest with a group of prominent elders from Jerusalem, all arrayed on the plaintiff's side of the court would IPSO FACTO be their "affirming" the charges. It is also likely that by voice response, or by some of them seconding the attorney's opening remarks, they effectively joined in the charges.

Evidently the high priest Ananias and the group were counting on the social prominence of the plaintiffs to sway the governor, for they brought no witnesses! Perhaps they considered themselves successors to the witnesses; but events proved that not even the pagan court of Felix would tolerate any such thing as a "successor" to witnesses. There is a message here regarding the claims of "successors" to the apostolic witnesses.