I have a case in which the defendant wrote a letter from jail to a third party, requesting him to "get rid" of my victim. somehow, my victim intercepted the letter. It's unclear to me whether under the Obstruction part of the statute the threat needs to be communicated to the victim. It seems clear that the threat must be communicated under the REtaliation portion but it's unclear under Obstruction. Any thoughts?

My experience regarding both is that the threat has to be communicated to the victim. I have investigated many of those type cases with similar results.

The threat doesn't necessarily need to be communicated to the victim, at least in retaliation cases. See LeBleu v. State, 192 S.W.3d 205 (14th Dist. - Houston, 2006). May give you a different view.