actions in the hours following the murder
What about his actions specifically?
the absence of an alibi
His Mother gives an alibi which they did not disprove in court and his brother never out right said Luke wasn't home so it's not the smoking gun for me as it is for you.
the conflicting statements
Conflicting statements and changing statements do a lot to make him look innocent too.
the eyewitness sightings
One damning eye witness but she doesn't identify him court. And gets so much wrong.
Mitchell's past conduct with a knife
He liked knives. A teenage boy? Unheard of.
he had the means, the motive and the opportunity to do it
Motive? What's his motive again? The secret girlfriend that Jodi didn't seem to know about or his disproved Marilyn Manson obsession?
Not bad for a first attempt.