A person can be held in contempt of court for lying in court. "Under penalty of perjury" is a reminder that the witness is under oath and that lying in court is punishable. If the witness takes this as a scare tactic to tell the truth, then it is a scare tactic. I would not consider this an empty threat, although it may be difficult to prove somebody was lying.
Marijuana is against federal law. Federal law supersedes state law. A person could be charged and convicted for marijuana related crimes such as possession, cultivation, distribution, manufacturing, transportation, and conspiracy.
It may be. If it is a sworn legal document, then perjury would be in play if it is a lie.
NEVER describe your facts in an online forum. I have CONFIRMED there is at least ONE county prosecutor that is a member of this site. My statements are my opinion solely based on the information provided, and that opinion can be wrong if your facts are different than what I believed them to be. If you have any further questions, you can contact me at 636-532-1400 or through my website http://mcmichael-logan.com