"They both ran, but the other disciple ran faster than Peter and arrived at the tomb first; he bent down and saw the burial cloths there, and the cloth that had covered his head, not with the burial cloths but rolled up in a separate place. Then the other disciple also went in, the one who had arrived at the tomb first, and he saw and believed." (John 20:4-8)
quoting from the Saverio Gaeta's book: L'altra Sindone, Mondadori, 2005, p. 19 (translation mine)
"Three simple words in the eighth verse 'he saw and believed' but enough to give rise in these 2000 years to innumerable biblical studies and exegetical interpretations... It is not enough to affirm as in various quarters it is proposed, that the absence of the body of Jesus had motivated the knowledge of the resurrection: on the contrary, at this point it would have been more obvious for John to share the opinion of Mary Magdalen regarding a theft.
In his Gospel John makes use of fully six verbs to indicate the act of vision: blepein, horan, opsomai, theasthai, theorein, and idein. And it is this last word that he adopts in chapter 20, verse 8, "he saw (eiden) and believed", a verb that, also in the other usages, "seems to suppose not a mere visual perception, becoming rather almost synonomous with 'believing". (*) In the brief affirmation there is almost a doubling of the concept, as one might say, as if John had wanted to reinforce to the maximum the significance of the three words."
* Ravasi, G., "Un Volta da contemplare", in Il Volto dei Volti: Cristo, edited by the Instituto Internazionale di Ricerca sul Volto di Cristo, Vol. VI, Editrice Velar, Gorle (BG) Italia, 2002, p. 43.