Some scholars have suggested an Aramaic background to Jesus’ saying. Joseph A. Fitzmyer, Professor Emeritus of The Catholic University of America in Washington, D.C., and one of the world’s most distinguished New Testament scholars, suggests that Jesus employed an Aramaic wordplay (Kepha-kepha) in his response to Peter’s declaration.[3] However, Fitzmyer acknowledges a difficulty: he wonders why the Matthean Jesus did not say, “On this petros I will build….”[4]
[4] Substituting the Greek masculine petros for the Greek feminine petra, the reading of all Greek manuscripts. See Fitzmyer, ibid., pp. 130-131: “The problem that confronts one is to explain why there is in the Matthean passage a translation of the Aramaic substratum, which is claimed to have the same word kepha twice, by two Greek words, πέτρος and πέτρα… If the underlying Aramaic of Matt. xvi.18 had kepha twice, then we should expect σὺ εἶ Πέτρος, καὶ ἐπὶ τούτῳ τῷ πέτρῳ οἰκοδομήσω….” Cf. Fitzmyer’s recent comments in response to a magazine reader’s letter (“Queries & Comments,”Biblical Archaeology Review 19.3 [1993], 70). For Fitzmyer’s Aramaic reconstruction to be correct, the Greek text should read, “on this petros I will build….”
[5] The word כֵּפָא (kepha). The only difference between Kepha and kepha in Fitzmyer’s reconstruction is the capitalization of the former. This distinction, however, does not exist in Aramaic, since in Aramaic there are no capital letters. - http://www.jerusalemperspective.com/2718/
Which is not the same as evidence.