Both instances of murder refer to an era that preceded the 613 commands of
the Mosaic law code.
The first mention of the appropriate punishment for a murder is in Genesis
4:11-15.
"And now art thou cursed from the earth, which hath opened her mouth to receive thy brother's blood from thy hand;...a fugitive and a vagabond shalt thou be in the earth.
And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him."
(KJV)
Adam and Eve's sons were Cain, a farmer, and Abel, a shepherd. Each brought
the best that they had had produced as a sacrifice to God. God accepted Abel's
sacrifice of meat but rejected Cain's grain offering. Cain's resultant
disappointment turned to anger; he killed his brother. God cursed Cain for the
murder and sent him to wander the earth. God also put a mark on Cain's body so
that nobody who saw him would be motivated to kill him. If anyone killed Cain
for the murder of his brother, that person would be very severely punished.
Here, banishment and exile is the penalty for murder; capital punishment is
specifically prohibited.
The first mention of capital punishment as a penalty for murder is in Genesis
9:6:
"Whoso sheddeth man's blood, by man shall his blood be shed: for in the image of God made he man."
(KJV)
This passage regards the killing of a human as an offense against God because
humans were made in the image of God, both male and female. Unlike the previous
passage which required that the murderer be merely exiled, this verse required
the murderer to be killed.
The Biblical books Exodus, Leviticus, Numbers and Deuteronomy
form the rest of the Pentateuch and contain the Mosaic Code - a set of civil and
religious transgressions with their appropriate punishments. This set of 613 laws greatly expanded the range of crimes which were punishable by death.
If sufficient proof were provided that a person had committed any of the
crimes listed below,
the state imposed the death penalty on the guilty person(s). They were either stoned to
death, impaled on a stick or burned alive. Witnesses who testified at the trial would often
participate in the killing.
To their credit, the courts of ancient Israel required very high levels of proof of
criminal behavior before they would order the death penalty.
"Death Penalty," Abounding Love Ministries, at: http://www.aboundinglove.org/
They list 42 activities for which the Hebrew Scriptures call for the
death penalty.