Yes, Cain killed Abel. He killed him with a forceful blow according to the Scriptures in Genesis 4:6-10. He slew Abel.
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Genesis 4
6 So the Lord said to Cain, “Why are you angry? And why has your countenance fallen? 7 If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is [d]for you, but you should rule over it.”
8 Now Cain [e]talked with Abel his [f]brother; and it came to pass, when they were in the field, that Cain rose up against Abel his brother and killed him.
9 Then the Lord said to Cain, “Where is Abel your brother?”
He said, “I do not know. Am I my brother’s keeper?”
10 And He said, “What have you done? The voice of your brother’s blood cries out to Me from the ground. 11 So now you are cursed from the earth, which has opened its mouth to receive your brother’s blood from your hand. 12 When you till the ground, it shall no longer yield its strength to you. A fugitive and a vagabond you shall be on the earth.”