I like the Christian apologist J. Warner Wallace. He talks about people not believing in the gospels thinking the gospel writers could have been influenced because they were sympathetic to Jesus and might have been biased. (Although Matthew became a Christ follower later without prior expectation of the Messiah). So he set about finding unfriendly writings that could at least confirm Christ lived and died. Some of the artlcles were from historians who quoted earlier writings that no longer exist but people still tend to believe them more because they were unfriendly to Jesus. J Warner Wallace was an athiest but he used his homicide detective skills to try to solve this cold case of Jesus. He admits that no one can prove the Case for Christ without any doubt but it can be proved beyond a reasonable doubt which is the standard of proof we use in trial. Trials that might send a person to death.
Here is the article about unfriendly pagan and Jewish writings about Jesus if you are interested.
http://coldcasechristianity.com/2014/is-there-any-evidence-for-jesus-outside-the-bible/
I'm familiar with those, but all were written in reaction to the rise of the Christian faith, and not by anyone who claimed to have known Jesus or witnessed any events recounted in the Gospels.