Professor Christian Troll, a Jesuit priest, has engaged in the studies of Islam since 1961. He is an influential scholar and a very well respected participant and Muslim-Christian conversation for decades. His books and numerous articles are a quest for mutual understanding. His website, Muslims Ask, Christians Answer is invaluable for both Christians and Muslims who want to come to a deeper respect and understanding of their respective faith traditions.
Muslims Ask, Christians Answer http://aam.s1205.t3isp.de/?L=1
The same material is available in paperback,
Article: “Muhammad – Prophet for Christians also?”
Towards common ground between Christians and Muslims? Professor Troll writes a response to “138 Muslim religious leaders call for reconciliation and cooperation with Christians.” His response is here:
Professor Troll’s main website: http://www.sankt-georgen.de/lehrende/troll.html (in German)