3 Let us hear, therefore, what follows: “When Saul sent and guarded his house in order that he might kill him.” This though not to the Cross of the Lord, yet to the Passion of the Lord does belong. For Crucified was Christ, and dead, and buried. That sepulchre was therefore as it were the house: to guard which the government of the Jews sent, when guards were set to the sepulchre of Christ. There is indeed a story in the Scripture of the Reigns, of the occasion when Saul sent to guard the house in order that he might kill David....But in like manner as Saul effected not his purpose of slaying David: so this could not the government of the Jews effect, that the testimony of guards sleeping should avail more than that of Apostles watching.
For what were the guards instructed to say? We give to you, they say, as much money as you please; and say ye, that while you were sleeping there came His disciples, and took Him away. Behold what sort of witnesses of falsehood against truth and the Resurrection of Christ, His enemies, through Saul figured, did produce. Enquire, O unbelief, of sleeping witnesses, let them reply to you of what was done in the tomb. Who, if they were sleeping, whence knew it? If watching, wherefore detained they not the thieves? Let him say therefore what follows.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)