Well, Mary Mandolin, and the other Mary saw it first, then they told the disciples. John and Simon saw it as well
"So she came running to Simon Peter and the other disciple, the one Jesus loved, and said, “They have taken the Lord out of the tomb, and we don’t know where they have put him!”
3 So Peter and the other disciple started for the tomb. 4 Both were running, but the other disciple outran Peter and reached the tomb first. 5 He bent over and looked in at the strips of linen lying there but did not go in. 6 Then Simon Peter came along behind him and went straight into the tomb. He saw the strips of linen lying there, 7 as well as the cloth that had been wrapped around Jesus’ head. The cloth was still lying in its place, separate from the linen. 8 Finally the other disciple, who had reached the tomb first, also went inside. He saw and believed. 9 (They still did not understand from Scripture that Jesus had to rise from the dead.) 10 Then the disciples went back to where they were staying."
Every time he says "the other disciple" that is actually John talking about himself in third person. It makes this story a bit more entertaining if you know that.
Of course, there are the roman guardsmen themselves:
"And when they had assembled with the elders and consulted together, they gave a large sum of money to the soldiers, 13and said, "You are to say, 'His disciples came by night and stole Him away while we were asleep.' 14"And if this should come to the governor's ears, we will win him over and keep you out of trouble."
(by the way, if the guards actually fell asleep, or were defeated by a couple of fishermen and an accountant, they probably would have killed themselves.)