Grievous complaints - Heavy accusations. Doubtless the same with which they had charged him before Felix, Acts 24:5-6. Compare Acts 25:19.
Which they could not prove - Acts 24:13, Acts 24:19.
Related Commentaries of Acts 25:7
Acts 25:7
7 And when he was come, the Jews which came down from Jerusalem stood round about, and laid many and grievous complaints against Paul, which they could not prove.