The investigation into the violent head-on train crash in southern Italy that killed nearly two dozen people is looking in particular into the antiquated telephone alert system used to advise station masters of trains running on the single track.

Recovery operations using a giant crane and rescue dogs continued through the night and into Wednesday to remove the mangled debris of the two commuter trains that slammed into one another in the neat olive groves between the Puglian towns of Andria and Corato.

Union leaders and railway police blamed human error, noting that that particular stretch of track didn't have an automatic alert system that would engage if two trains were close by on the same track. Rather, news reports said the alert system relied on station masters phoning one another to advise of a departing train.