Baruch.. man of noble family (Jeremiah 32:12) suspected here. The reason may be found in Jeremiah 45:1-5.
Related Commentaries of Jeremiah 43:3
Jeremiah 43:3
3 But Baruch the son of Neriah setteth thee on against us, for to deliver us into the hand of the Chaldeans, that they might put us to death, and carry us away captives into Babylon.