I don't beleive there is any documented proof, but Leandro Lara claimed he was a son to Jack Swilling. Jack was in the right place to be his father, so it is possible. If the Catholic church has a record of Leandro's birth or Christening, that may tell who his father was. Other than that, you could say there is a strong family tradition, citing the information found on his death certificate, and the informants relationship.