A.T. Robertson Commentary John 19:33

"but when they came to Jesus, and saw that he was dead already, they brake not his legs:" — John 19:33 (ASV)

Already dead (ηδη τεθνηκοτα). Perfect active participle of θνησκω. So then Jesus died before the robbers, died of a broken heart.

They brake not (ου κατεαξαν). The augment is proper here (see 32).