וַיֹּ֣אמֶר אֲבִימֶ֔לֶךְ לֹ֣א יָדַ֔עְתִּי מִ֥י עָשָׂ֖ה אֶת־הַדָּבָ֣ר הַזֶּ֑ה וְגַם־אַתָּ֞ה לֹא־הִגַּ֣דְתָּ לִּ֗י וְגַ֧ם אָנֹכִ֛י לֹ֥א שָׁמַ֖עְתִּי בִּלְתִּ֥י הַיּֽוֹם׃
Da sprach Abimelech: Ich weiß nicht, wer das getan hat. Du hast mir nichts davon gesagt, auch habe ich bis heute nichts davon gehört.
Sforno on Genesis
לא ידעתי מי עשה, even now that you have informed me by means of my servants that you have been unjustly victimised, I still do not know who are the ones who could have done this. Not a single one among the people concerned seems suspect to me. Had I suspected any one of my servants of such conduct he would not have been tolerated in my entourage.
Or HaChaim on Genesis
ויאמר אבימלך…וגם אנכי, Avimelech said: "Also I have not heard, etc." The words: "also I," need clarification; so do the words: "who has done it." All Avimelech needed to say was "I did not know."
Radak on Genesis
ויאמר...וגם אנכי לא שמעתי, seeing that neither you nor anyone else has told me about this I cannot be held responsible for this.