It is in Genesis, chapter four, that we learn of the first two children of Adam and Eve.  They were Cain and Abel.  We read in verses 3-5, “And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering: But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.”  As Cain and Abel grew and realized their responsibility towards the Lord, they both brought offerings to the Lord.  Cain brought the fruits and vegetables he had grown, and Abel brought “the firstlings of his flock and of the fat thereof” which indicates he killed this animal as a sacrifice to the Lord. We read in Hebrews 11:4, “By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaketh.”  Abel, by faith, brought to the Lord what He desired, and the Lord had respect unto that sacrifice…declaring Abel to be righteous. 

We read that Cain was “very wroth, and his countenance fell.”  What does that mean?  The Amplified Bible says that Cain “became extremely angry (indignant), and he looked annoyed and hostile.”  Cain was infuriated that the Lord rejected his offering but accepted Abel’s.  We then read in verse 8 that, “Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.”  We have no idea what Cain said to his brother, so we do well not to speculate.  It was later, when they were both in the field that Cain killed Abel.  Envy is a very destructive devise, and it led to the death of Abel.  How sad that the first person ever born became the first murderer.  How great is sin in the heart of man that it knows no boundary…a man would kill because of jealousy!

You asked who else was present in Eden that witnessed this murder.  First of all, this did not happen in Eden.  After Adam and Eve sinned in the Garden of Eden, they were cast out and were blocked from ever entering it again.  We read in Genesis 3:22-24, “And the LORD God said, Behold, the man is become as one of us, to know good and evil: and now, lest he put forth his hand, and take also of the tree of life, and eat, and live for ever: Therefore the LORD God sent him forth from the garden of Eden, to till the ground from whence he was taken. So he drove out the man; and he placed at the east of the garden of Eden Cherubims, and a flaming sword which turned every way, to keep the way of the tree of life.”  What an act of grace by our loving Lord.  To prevent Adam from eating from the tree of life, and live forever in his sinful state, the Lord prevented that by sending them out of the garden and having Cherubims guard the entrance. 

Who witnessed this murder?  I suppose you wonder how we know about it unless someone witnessed it.  Surely Adam and Eve knew their son had been killed.  Certainly, the Lord knew about it and confronted Cain.  “And he said, What hast thou done? the voice of thy brother’s blood crieth unto me from the ground. And now art thou cursed from the earth, which hath opened her mouth to receive thy brother’s blood from thy hand; When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth.” (Genesis 4:10-12).  He drove Cain from the land, causing him to be a wanderer for the rest of his days.  What a sad result of sin!  Verse 16 tells us, “And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden.”

The murder of Abel was well known and is mentioned in the New Testament.  1 John 3:12 says, “Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother’s righteous.”  The story of Abel’s faith is also mentioned. Hebrews 11:4 says, “By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaketh.”  (CC)  (675.4)