No one even knows for sure how Paul died.
Agreed.
There's a tradition that he died in prison,
Never heard of this, not saying it doesn't exist.
and another tradition that he was beheaded.
The key word here is "tradition". 2Timothy has Paul saying his death is eminent. A "tradition" is something that the generation in question accepted as fact, followed by every successive generation. A "legend" is a story that the generation in question rejected as fact BUT later re-appeared in other generations. The tradition of Paul's beheading is a tradition accepted by multiple quarters of christendom, from the British church, Rome, Jerusalem, and of course Antioch. These are compelling lines of evidence SINCE, in the 1st century, NO modern communication abilities existed. Such a "tale" would have never made it past Rome. The tradition of Paul's beheading is a fact, although Dr. Scott says there is ample evidence it actually came well after 2Timothy - that being a false alarm.
Brian: are truth and accuracy synonymous ?
But, there is no external contemporary evidence of Paul's death. Having said that, there is no external evidence of any apostle's death either.
By traditions and legends there is.
While I degraded "legends" above; all are NOT untrue. If the legend corresponds with unconnected facts then historians have a basis.
Legend says Thomas was martyred near Madras, India. The legend is supported by the fact that there is an ancient church at Mt. St. Thomas, India. The fact that we are talking INDIA shows there can be no bias since that land is ruled by non-christians.
In addition, there exists NOT ONE shred of evidence contradicting any martyrdom legend or tradition. If the accounts are not true THEN surely history would betray and cough up something - yet nothing, zero, zip.
Ray