Headscratchers / Better Watch Out

• Why would Luke use Garrett's body as part of his staged crime scene? His alibi was supposed to be that he was in bed the whole time and slept through "Jeremy's" rampage. Luke's parents saw Garrett leave the house; he left when they did. He's Luke's friend, so Luke is the only reason he'd still be at the house. Why would he come back after Luke would supposedly already be fast asleep? Assuming Luke absolutely couldn't have just hidden his body and disposed of it later, it would have at least made more sense to have it placed outside, to make it look like Garrett was on his way back to see Luke, not knowing that he was already asleep, when he saw Jeremy and became his first victim of the night.
  • Because Luke is not as clever as he thinks he is. His plan fails to account for modern police forensic techniques, like testing for gunshot residue (which won't be on the supposed killer), blood spatter patterns (which won't match what supposedly happened) and so on. Luke would probably have been temporarily deafened by the shotgun blast and it's also very unlikely that he managed to remove all trace of himself from the bodies and murder weapons. Did he even burn his clothes or take a shower afterwards? Also, it's been a while since I watched the movie, but it seemed that killing Garrett wasn't originally part of the plan and he just did it in a fit of rage.