Complex sentence: He is regarded as authoritative representatives of the ecumenical between Christianity and Islam, although 19 religious murdered occurred between 1994 and 1996 during which Pierre Claverie, the Bishop of Oran died and monks of Tibhirine took place.
Split into simpler sentences: He is regarded as one of the authoritative representatives of ecumenism between Christianity and Islam, despite 19 murders of non-muslim religious people occurred between 1994 and 1996. During this period Pierre Claverie, the Bishop of Oran was killed and monks of Tibhirine took place.