Richard Bauckham's book Jesus and the Eyewitnesses
, (Eerdmans 2006) is highly recommended for its painstaking historical research and its clear demonstration that the four Gospels of the New Testament are indeed the testimony of eyewitnesses.
Bauckham and other scholars are responsible for a new wave of conservative New Testament research that not only stems the impure tide of writings that attempted to destroy the credibility of the canonical Gospels in the past century or so, but he also brings the kind of recovery of truth that makes for times of great spiritual refreshment.
In his characteristic thoroughness, Bauckham also makes a stunning case for the Fourth Gospel being authored by an ideal witness (the beloved disciple), someone other than the traditionally assumed author.
This book is well worth reading if you're serious about the Scriptures. Though some may find it academic at times, it is well worth disciplining onself to read it through with comprehension, and the reward will be a deeper appreciation for the Word of Truth which God has preserved for us in the unrestricted kindness of His Providence.