Pliny's letter to Trajan, 80 years or so after the alleged death of Jesus, mentions "Christ" several times but not in an historical context. Christianity was already in existence and Pliny was referring to their Christ, not to a figure whose historicity he was confirming in any way. The Mara Serapion letter is of uncertain date. It does not mention the name of the "wise king of the Jews", who he regards as having been unjustly executed, and the letter appears to contradict the resurrection. There really is very little in it to hang on to.   The Suetonius reference is very odd and is the subject of many an historian-style squabble. Suetonius knew about "Christians" and it is unlikely that he would have made the careless misspelling "Chrestus". Chrestus was a very common name in Rome and the passage could just be referring to an agitator called Chrestus in Rome.

I'm not saying that these are not interesting sources. They are. But not a single one fits the bill as an undisputed, or even mildly disputed, non-Christian reference to Jesus. Read all about 'em - they're all over google, as you'd expect. They might not exactly be clutching at straws but they're not far off, and good evidence of the certainty of Jesus's existence is still eluding you.