Great question!
I am a Christian and I will answer best I can.
The verse I'm assuming you're referring to is
1 John 3:15 - which states:
"Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him."
This was the disciple John teaching to the saved saints of God regarding his bretheren in Christ. The saints of God cannot be held accountable at the same level as those who do not have the truth. The saints of God are set apart to the Gospel (Rom 1:1)
we all will be held accountable for what we know, and what we do with what we know. Saints are not to judge those who dont have the truth, but those among them who do.
This verse is talking about one whose heart is full of hate because they do not have God's Spirit- that they still can be forgiven... but those who have God's Spirit already, would not abide in that murderous/haterd spirit.
Someone like Casy Anthony does not know God like those with His Holy Spirit know Him. She lives in darkness. In a different spiritual realm than those who know Christ. James 4:4 says "Anyone who chooses to be a friend of the world becomes an enemy of God."
The Bible is clear on sin. Whether there be one sin, or 100, you cannot make it to Heaven without having repented, being washed, and having received the Spirit of God- and being faithful to the Word- doing the Will of God (Matt 7:21).
But, there are Scriptures that talk of degrees of sin.
Like in John 19:11, Jesus told Pilate that those who delivered Him unto Pilate had the greater sin.
And then there are Scriptures that speak of those who will receive "greater condemnation" (Mt. 23:14; Mark 12:40; Luke 20:47; James 3:1).
Rom 6:23 tells us the wages of sin is death.
And those who live by the sword will die by the sword. (Matt 26:52).
There are also sins that are abominations to the LORD. The word "abomination" in the original text means it "disgusts" the Lord.
In Revelation 3:16 God shows how much he loathes complacency. "So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth". that word spue means "vomit". And witchcraft and occult practic angers God, the Word says.
So, there are degrees, but all are held accountable for their deeds.
I heard someone ask- "would those people be just as angry if Casey Anthony aborted Caylee before she was born?" Murder is murder, right?
It all depends on how we view it...but there is only one judge, and that is God.
If I lie, and you kill, we both and doomed to hello- unless we do what is required of us for salvation (Mark 16:16) and being in the Will of God.