Regardless of whether they are a police officer or a civilian, no one should be above the law. Police officers are bound by law and the Constitutions and statutes of the United States and the State of Texas, and must follow those laws.
The law that prevents excessive use of force is found at Chapter 42, Section 1983 of the United States Code, and is often referred to merely as "1983" This law makes it illegal for an agent of the federal, state, or municipal government to improperly deprive someone of civil rights under authority of law.
What determines whether a police officer's actions violate the law? THe answer comes down to a question of reasonableness. If the officer reacted unreasonably, given what the officer knew at the time, then the officer may be held liable for injuries that resulted. You may also be able to recover attorneys fees.
1983 cases are hard. They must be filed in federal court, and very often are difficult cases to win, just because there is a natural tendency for juries to want to believe what police officers say. That being said, you should definitely contact an attorney about the specific facts of your situation to discuss whether it would be adviseable or appropriate to pursue legal action based on the facts of what happened to your family member.
Please feel free to contact me if you have more questions.
It sounds he may have a good case for false arrest, malicious prosecution and excessive force.. See my legal guide.