Nigeria abductions: Boko Haram video 'can help find girls'
13 May 2014 Last updated at 11:34 BST
Forensic analysis of a Boko Haram video showing about 130 schoolgirls kidnapped by the militant Islamist group could provide clues to their location, forensic video analyst Grant Fredericks has said.
Mr Fredericks told the Today programme that investigators would be able to narrow down possible locations for the girls by studying the vegetation and shadows in the video, as well as the fabric of the banners being held.
First broadcast on BBC Radio 4's Today programme on Tuesday 13 May.