Many of the Christians I know are aware that the fourth gospel contains an explicit claim to be written by an eyewitness: "This is the disciple who testifies to these things and who wrote them down" (John 21:24). This is common knowledge among Christians who discuss the Bible with non-Christians; it is basic "Apologetics 101" level material. Yet the charge has been circulating that no gospels claim to have been written by an eyewitness. This charge bears the marks of someone who is simply not that familiar with the material.
This claim has been made by Bart Ehrman. In his book Lost Christianities he asserts that none of the canonical gospels "claims to be written by an eyewitness or a companion to an eyewitness" (p. 135 of the 2003 Oxford U. printing available at my library).
It is unfortunate that his book contains a misstatement of fact that could have been easily avoided by a more thorough knowledge of the subject. Sometimes, when meeting claims against Christianity, it helps to remember that the level of Biblical literacy in our society is at very low levels, and some patience is called for as we seek to inject some more knowledge of the texts into the current discussions about them.