In Exodus 12:23 (NASB)
For the Lord will pass through to strike the Egyptians; but when He sees the blood on the lintel and on the two doorposts, the Lord will pass over the door and will not allow the destroyer to come in to your houses to strike you.
In Psalms 78:49 (NASB)
49 He sent His burning anger upon them,
Fury and indignation and trouble, A band of destroying angels.
50 He leveled a path for His anger; He did not spare their souls from death,
But turned their lives over to the plague,
51 And struck all the firstborn in Egypt,
The first and best of their vigor in the tents of Ham.
Was it "A band of destroying angels" that killed the firstborn?
There's a similar question (with an already accepted answer that considers mostly Exodus) but it's not in its scope Psalms 78.