2 Chronicles 30:17

For there were many in the convocation, who had not hallowed themselves, - but, the Levites, were over the slaughtering of the passover-lambs, for every one who was, not pure, to hallow him unto Yahweh.

2 Chronicles 29:34

Only, the priests, were too few, and were unable to flay all the ascending-sacrifices, - so their brethren the Levites strengthened them, until the work was complete and until the priests had hallowed themselves, for, the Levites, were more upright in heart to hallow themselves, than the priests.

Exodus 12:6

So shall it be yours, to keep, until the fourteenth day of this month, - then shall all the convocation of the assembly of Israel slay it between the two evenings.

2 Chronicles 35:3-6

and said to the Levites who gave instruction to all Israel as to the things which were hallowed unto Yahweh, Put the holy ark in the house which Solomon son of David king of Israel did build, it is not yours as a burden on the shoulder, - Now, serve ye Yahweh your God, and his people Israel;

Treasury of Scripture Knowledge

Summary

For there were many in the congregation that were not sanctified: therefore the Levites had the charge of the killing of the passovers for every one that was not clean, to sanctify them unto the LORD.

The killing

Bible References

The levites

2 Chronicles 29:34
Only, the priests, were too few, and were unable to flay all the ascending-sacrifices, - so their brethren the Levites strengthened them, until the work was complete and until the priests had hallowed themselves, for, the Levites, were more upright in heart to hallow themselves, than the priests.
2 Chronicles 35:3
and said to the Levites who gave instruction to all Israel as to the things which were hallowed unto Yahweh, Put the holy ark in the house which Solomon son of David king of Israel did build, it is not yours as a burden on the shoulder, - Now, serve ye Yahweh your God, and his people Israel;

The killing

Exodus 12:6
So shall it be yours, to keep, until the fourteenth day of this month, - then shall all the convocation of the assembly of Israel slay it between the two evenings.