This will likely be allowed by free speech and fair use as news and commentary. However, you should consult a Texas licensed IP attorney (I am one, and there are others active here on Avvo) for specific review and clearance.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
It will largely depend on what you use and the context of that use. Just because you are making a movie about this subject does not mean that you are free to use any and all footage you find. If, for example, that was some iconic footage associated with that event then I would likely agree that its use in this context would be fair.
I suggest that you consult with a lawyer in private and discuss your objectives in more detail. You may prefer to use a local lawyer, but you are free to hire a lawyer anywhere so you have options. You can start by calling around to several for a free phone consultation, get some insights then pick the best fit to work with.
DISCLAIMER: this is not intended to be specific legal advice and should not be relied upon as such. No attorney-client relationship is formed with the law firm of Natoli-Lapin, LLC on the basis of this posting.
You should read the information about copyright and fair use for documentary film makers via the link below and then speak with your own Texas-licensed intellectual property attorney. Good luck.
The above response is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.