Why did Arjuna not kill Kripacharya in the Mahabharata War?

Why did Arjuna not kill Kripacharya in the Mahabharata War? On 14 th day after Jayadratha’s death,Kripacharya and Aswathama attacked Arjuna and got injured in turn. Baffling with his own weapons those of both Aswatthaman and Kripa, he sped at them, without desiring to slay them, shafts that coursed mildly. Those shafts, however (though mildly), shot by Jaya struck the two with great force, and in consequence of their number, caused great pain to Kripa and his nephew. CXLVI Drona parva Kripa swooned on the terrace of his chariot and lost consciousness.Aswathama fled away in fear from Arjun. Kripa was taken away by his charioteer. Then Saradwat's son, O king, thus afflicted with the arrows of Arjuna, lost all strength and swooned away on the terrace of his car. Understanding his master afflicted with shafts to be deprived of his senses, and believing him to be dead, the driver of Kripa's car bore Kripa away from the fight. And after Kripa, the son of Saradwat, had thus been borne away from the battle, Aswatthaman also, from fear, fled away from the son of Pandu. CXLVI Drona parva Arjuna’s grief Arjuna grieved on seeing his preceptor Kripa’s state . Shedding tears he lamented..that because of Duryodhan,he has to see the destruction of his race and his preceptor lying injured by his arrows. Then the mighty bowman, Partha, beholding the son of Saradwat afflicted with shafts and in a swoon, began to indulge, on his car, in piteous lamentations. With a tearful face and in great dejection of heart, he uttered these words: Alas, these words of the truth-telling Vidura have come to be true. It is for him that I behold my preceptor today lying on a bed of arrows. Fie on the practices of Kshatriya! Fie on my might and prowess! Who else like me would fight with a Brahmana that is, besides his preceptor? Kripa is the son of a Rishi; he is, again, my preceptor; he is also the dear friend of Drona. Alas, he lieth stretched on the terrace of his car, afflicted with my arrows. CXLVI Drona Parva Arjun said he will go to hell for injuring his preceptor. Those bulls among men that give desirable objects unto their preceptors after obtaining knowledge from them, attain to godhead. Those lowest of mortals on the other hand, who, after obtaining knowledge from their preceptors strike the latter, those wicked men, go to hell. Without doubt, this act that I have done will lead me to hell. I have deeply pierced my preceptor on his car with showers of arrows. CXLVI Drona parva Arjuna remembered Kripa asking him not to strike the preceptor ever but he regretted disobeying his word. While studying the science of arms at his feet, Kripa told me in those days, 'Do not, O thou of Kuru's race, ever strike thy preceptor. That command of my righteous and high-souled preceptor I have not obeyed, for I have struck, the very Kripa himself with my shafts. I bow to that worshipful son of Gotama, to that unretreating hero. Fie on me, O thou of Vrishni's race, since I have struck even him.' CXLVI Drona parva This was how Arjuna reacted when he struck Kripa mildly,not even aggressively. He felt guilty of giving pain to his preceptor Kripa who trained him in war fare knowledge after getting initiated by Shukra,son of Saryati at Satasringa mountain and before Drona got appointed as preceptor by Bhishma . come what may Arjun would never have killed either Kripa or Drona or even Aswathama. He always fought mildly with them with half his mettle. Such Arjun who couldn’t even bear with Kripa getting injured by his arrows,would kill him ever? Not possible. He may accept defeat,loss of kingdom but could never kill his preceptors who nourished him,trained him and made him the greatest warrior of the times! My answer is based on story of Vyasa Bharat