Excerpt from Gesta Francorum:
(Quos dux persequens invictus cum Christi militibus septem ex illis occidit, persequendo alios usque ad portam civitatis)
= When the invicible Duke pursuing them with army of Christ, he killed seven of them, and (when pursuing) he killed the others near the gate of the town
Persequendo is Gerundive, here it is used in Ablative case - seems strangle, and it is Deponent Verb. I guessed it ...