Cain and Esau
The first human murder, committed by Cain upon his brother Abel, was an act of evil premeditation. It was not a matter of unlawfully killing someone in a sudden confrontation, but a deliberate, calculated execution of his own brother - after the LORD (see Christ The Creator) told him to cool down from his jealousy.
"4:3 And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. 4:4 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: 4:5 But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.
"Esau said in his heart, The days of mourning for my father are at hand; then will I slay my brother Jacob"
Cain apparently didn't tell anyone about his plan to commit murder - his parents were likely the only other humans in existence at that point anyway (or perhaps the only other adult humans in existence at that point), so it was hardly a matter of Cain being able (no pun intended) to keep something in confidence. The same cannot be said of another jealous brother of Bible History, Esau, who would also have committed premeditated murder of his brother, Jacob. Esau boasted of his plan to kill his brother, a factor that ironically saved his intended victim's life.
"27:41 And Esau hated Jacob because of the blessing [see Blessing The Favorites and Why Did Esau Lose The Blessing?] wherewith his father blessed him: and Esau said in his heart, The days of mourning for my father are at hand; then will I slay my brother Jacob.
It's interesting that Rebekah had to use another ruse to get Jacob away from Esau. Rather than telling Isaac that one of his sons was planning to kill the other, Rebekah used an excuse (albeit a legitimate one) of finding a wife for Jacob from the family homeland back in Iraq.
"27:46 And Rebekah said to Isaac, I am weary of my life because of the daughters of Heth: if Jacob take a wife of the daughters of Heth, such as these which are of the daughters of the land, what good shall my life do me?" (Genesis 27:46 KJV)
So Jacob was sent away to Rebekah's brother for what Rebekah thought would be only a relatively brief stay ("27:44 And tarry with him a few days, until thy brother's fury turn away" Genesis 27:44 KJV). It would however be over twenty years (Genesis 31:38) before Jacob returned home to the land that would be named after him - the LORD (see 'Before Abraham Was, I AM') changed Jacob's name to Israel during the return journey (Genesis 32:28).
"28:1 And Isaac called Jacob, and blessed him, and charged him, and said unto him, Thou shalt not take a wife of the daughters of Canaan. 28:2 Arise, go to Padanaram, to the house of Bethuel thy mother's father; and take thee a wife from thence of the daughters of Laban thy mother's brother. 28:3 And God Almighty bless thee, and make thee fruitful, and multiply thee, that thou mayest be a multitude of people; 28:4 And give thee the blessing of Abraham, to thee, and to thy seed with thee; that thou mayest inherit the land wherein thou art a stranger, which God gave unto Abraham. 28:5 And Isaac sent away Jacob: and he went to Padanaram unto Laban, son of Bethuel the Syrian, the brother of Rebekah, Jacob's and Esau's mother." (Genesis 28:1-5 KJV)
Fact Finder: (a) When and where were nearly all of Jacob's children born? (b) Which of Jacob's children was the only one to be born in the land that became known as Israel?