In Matthew 14:2 & 8, we find the same Greek Word,  βαπτιστης, (4/12, 5/12).  It is in this passage that we read of John's death at the hand of Herod. He was put to death because the King in his lust promised to deliver to his niece anything that she so desired.  Her mother told her to ask for the head of John the Baptist. There are no Baptisms taking place around these verses.

Matthew 16:14 also has βαπτιστης (6/12), but in this context it is in relation to who people claim Jesus is. 

Matthew 17:13 is a passage once again that does not have Baptism, but does refer to John the Baptist, βαπτιστης (7/12).  Here Christ identifies him as Elijah who was to come. This should help stop any doubts a person might have as to whether or not John's baptism was from Heaven or from man.