Complex sentence: He infiltrated the fuselage survivors, posing as one of them, until they discovered his true identity, at which point he kidnapped Charlie Pace and the pregnant Claire Littleton, attempting to dispose of the former soon after.
Split into simpler sentences: He infiltrated the fuselage survivors, posing as one of them until they discovered his true identity. He then kidnapped Charlie Pace and the pregnant Claire Littleton, attempting to dispose of the former soon after.