Did the fruit from the tree of the knowledge of good and evil kill Adam and Eve?  God commanded Adam and Eve not to eat from it and if they did then they would surely die.

Gen 2:16  And the LORD God commanded the man, saying, “Of every tree of the garden you may freely eat;
Gen 2:17  but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.”

From these two verses many people believe that the cause of death of Adam and Eve was the fruit from the tree of the knowledge of good and evil.  But this is actually an assumption.  The Scriptures do not say that.  They say that if Adam and Eve ate of the fruit they would die, but it does not state what the cause of death would be. 

Unfortunately, Adam and Eve ate from it.

Gen 3:6  So when the woman saw that the tree was good for food, that it was pleasant to the eyes, and a tree desirable to make one wise, she took of its fruit and ate. She also gave to her husband with her, and he ate.

Several verses later we are told the cause of death after they had eaten the fruit.

Gen 3:22  Then the LORD God said, “Behold, the man has become like one of Us, to know good and evil. And now, lest he put out his hand and take also of the tree of life, and eat, and live forever”—
Gen 3:23  therefore the LORD God sent him out of the garden of Eden to till the ground from which he was taken.
Gen 3:24  So He drove out the man; and He placed cherubim at the east of the garden of Eden, and a flaming sword which turned every way, to guard the way to the tree of life.

God banished Adam and Eve from the garden lest they ate of the tree of life and lived forever.  This means it was possible for them to live forever after eating from the tree of the knowledge of good and evil if they also ate from the tree of life. 

The fruit from the tree of the knowledge of good and evil did not kill Adam and Eve.  What killed Adam and Eve was being denied access to the tree of life.  Eating the fruit of the tree of life was symbolic of receiving the Holy Spirit.  Having the Holy Spirit dwelling in us is essential for receiving eternal life.

Rom 8:11  But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you.

After eating the forbidden fruit, Adam and Eve were denied access to the Holy Spirit and their chance to receive eternal life.  (They are not lost forever.  They will be resurrected to physical life in the second resurrection where they will have the opportunity to obey God along with the vast majority of mankind.  They did however, miss out on being resurrected to eternal with the saints when Jesus Christ returns.)

What killed Adam and Eve was being denied access to the tree of life which meant being denied access to receiving the Holy Spirit.