There are lots of posts out there about the horrifying Eckert case (including mine), and lots of them are good, but you should definitely read this one posted today by Ken White at Popehat, entitled "What Is The Quantum of Proof Necessary for Police to Rape and Torture You in New Mexico?"
As usual, Ken pulls no punches (including in his headlines). He analyzes the affidavit that was used to justify the search warrant (itself an interesting read for different reasons) that was used to justify the repeated anal intrusions, and concludes:
It really comes down to three things: (1) subjective officer impressions that Eckert looked nervous, (2) a dog alerting on his [car] seat, and (3) an unnamed cop making an unspecific claim that he had previously hidden drugs in his anus.
Those hardly add up to probable cause, at least given that there was no corroboration for the anonymous "tip," he points out.
One thing I will add about that: the assistant DA who approved the warrant is a defendant, and in his answer to the complaint he says he doesn't know who told the officers that Eckert was "known in Hidalgo County to carry drugs in his anus," and so denies that allegation. But he admits that Eckert was in fact "known in Hidalgo County to carry drugs in his anus." He doesn't say where he obtained this knowledge of what was known about the anus in question, though.
Anyway, you should read the post, which is an excellent analysis of the case (based on what we know so far) and of why, exactly, it is so terrifying. Beyond the obvious, that is.