Can I suggest that the problem you have is not so much that the death of Christ appears to be a direct consequence of an act of breaking Gods Law i.e. murder,therefor how can a lawless act be given the credit of being interpreted as an act of Salvation? But rather you have an issue with the doctrine of the absolute sovereignty of God.

True Theology puts God center as Sovereign Creator and absolute authority in governing the affairs of man. He has the ultimate right to do with sinful humanity as he sees fit. If man lives in disobedience to him, then he has every right to use even those acts of defiance to further his Glory and purpose-albeit those who prosecute such acts will face His judgement in eternity.cf Romans 9:17-18,22.Also 19:11 Rev 1:7

This presupposes that all the acts of men, even those who reject God and do things in willful sin and ignorance, are ultimately directed to the overall purpose and intent of God-even if these intentions are wicked. This as opposed to those, by the same token that are for his good purpose.cf Gen 50:20,Phil 2:13 Eph 2:8,9.

This principle is seen again in Acts 2;23, In respect of the human intent and Gods purpose. Another member has mentioned the fact that Christ submitted himself willingly to his executioners and that He recognized and affirmed, even secular authority as being an unwitting instrument of his Father. Gal 1:4 also John 19:9-11.