quote:
48“Am I leading a rebellion,” said Jesus, “that you have come out with swords and clubs to capture me? 49Every day I was with you, teaching in the temple courts, and you did not arrest me. But the Scriptures must be fulfilled.” 50Then everyone deserted him and fled.

Now, this is the one and only place in all of the Gospel of Mark that says anything about scriptures being fulfilled (except another instance in Mark 15 which is a widely acknowledged later modification because it is not in the earliest manuscripts).

So in the Gospel of Mark there are hundreds of parallels to the Jewish scriptures, and nowhere else in Mark it is said that anything happened in order to fulfill the scriptures, even though the events of the scenes parallel the scriptures. But in Matthew, over and over again Matthew calls out these parallels and says that they happened in order to fulfill scripture.

So this appears to be a fairly transparent case of Mark being conformed to Matthew by the original editor of the collection. We can ask, why only here and nowhere else? But we could ask teh same thing about the modification in Mark 15:27 They crucified two robbers with Him, one on His right and one on His left. 28 [And the Scripture was fulfilled which says, “And He was numbered with transgressors.”]

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if mark was making parallels of his story to jewish scriptures and was using matthew as a source in the process, you would expect mark would have had more than one place where he writes about the fulfilment ,”taken place to fulfill the scriptures” ?