Isn't any arrest which is not legally justifiable an illegal arrest?
http://legal-dictionary.thefreedictionary.com/Unlawful+Arrest
You may try
Sec. 20.02. UNLAWFUL RESTRAINT. (a) A person commits an offense if he intentionally or knowingly restrains another person.
(b) It is an affirmative defense to prosecution under this section that:
(1) the person restrained was a child younger than 14 years of age;
(2) the actor was a relative of the child; and
(3) the actor's sole intent was to assume lawful control of the child.
(c) An offense under this section is a Class A misdemeanor, except that the offense is:
(1) a state jail felony if the person restrained was a child younger than 17 years of age; or
(2) a felony of the third degree if:
(A) the actor recklessly exposes the victim to a substantial risk of serious bodily injury;
(B) the actor restrains an individual the actor knows is a public servant while the public servant is lawfully discharging an official duty or in retaliation or on account of an exercise of official power or performance of an official duty as a public servant; or
(C) the actor while in custody restrains any other person.
(d) It is no offense to detain or move another under this section when it is for the purpose of effecting a lawful arrest or detaining an individual lawfully arrested.
(e) It is an affirmative defense to prosecution under this section that:
(1) the person restrained was a child who is 14 years of age or older and younger than 17 years of age;
(2) the actor does not restrain the child by force, intimidation, or deception; and
(3) the actor is not more than three years older than the child.
or
Sec. 39.03. OFFICIAL OPPRESSION. (a) A public servant acting under color of his office or employment commits an offense if he:
(1) intentionally subjects another to mistreatment or to arrest, detention, search, seizure, dispossession, assessment, or lien that he knows is unlawful;
(2) intentionally denies or impedes another in the exercise or enjoyment of any right, privilege, power, or immunity, knowing his conduct is unlawful; or
(3) intentionally subjects another to sexual harassment.
(b) For purposes of this section, a public servant acts under color of his office or employment if he acts or purports to act in an official capacity or takes advantage of such actual or purported capacity.
(c) In this section, "sexual harassment" means unwelcome sexual advances, requests for sexual favors, or other verbal or physical conduct of a sexual nature, submission to which is made a term or condition of a person's exercise or enjoyment of any right, privilege, power, or immunity, either explicitly or implicitly.
(d) An offense under this section is a Class A misdemeanor.
There are probably more bountiful and/or more applicable federal laws, as well. Would you like for me to look into that for you?