This is unique to Matthew, who remarked that Pilate said to them (ἔφη αὐτοῖς ὁ Πειλᾶτος), the chief priests and the Pharisees, that they had a guard of soldiers or custodians (Ἔχετε κουστωδίαν·). They could make this tomb as secure as they knew how or could (ὑπάγετε ἀσφαλίσασθε ὡς οἴδατε). Thus, these Jewish leaders secured the tomb (οἱ δὲ πορευθέντες ἠσφαλίσαντο τὸν τάφον) by sealing the stone (σφραγίσαντες τὸν λίθον) that was in front of the tomb and setting up a custodial guard (μετὰ τῆς κουστωδίας). Thus, it was not a Roman guard but a Jewish guard at the sealed tomb.
Thus, we have the prophetic statement of Gabriel. The terminology here is weeks and not years. Jeremiah had used 70 years. 7 was generally a complete or perfect number. Therefore, the popular terminology developed about lucky 7. During these 70 weeks or 70 years, they would make up for all the transgressions of the people and the holy city. Does 70 weeks imply 70 years times a week of 7, or 490 years? This time would atone for their sins and their iniquities. This would then bring about an everlasting righteousness, sealing both the vision and the prophet. Thus, they could anoint this holy place at the end of this period.