וְגַ֤ם דַּֽם־הַנָּקִי֙ אֲשֶׁ֣ר שָׁפָ֔ךְ וַיְמַלֵּ֥א אֶת־יְרוּשָׁלִַ֖ם דָּ֣ם נָקִ֑י וְלֹֽא־אָבָ֥ה יְהוָ֖ה לִסְלֹֽחַ׃
und auch für das unschuldige Blut, das er vergoss; denn er füllte Jerusalem mit unschuldigem Blut; und der Herr würde nicht vergeben.
Ralbag on II Kings
and the LORD would not pardon: This means that even though Menasseh repented, God was not willing to forgive his spilling of innocent blood. And it would seem that this included servants of the Lord - that he killed Isaiah son of Amoz because of how he reproached him. And thus our teachers of blessed memory said that Menasseh killed Isaiah.