Reports from other sources say that as many as 40 people have been detained, 20 of them women. The violence started when the protesters surrounded the PFP, Mexico's Preventative Federal Police, in the main square, or Zocalo. Then the PFP and their PRIista allies began firing into the crowd who was armed with stones and Molotov cocktails. The plain clothed PRIistas are presumably the men in taxis tossing tear gas canisters into the frantic crowds.
PRIistas are members of the P.R.I. or Institutional Revolutionary Party, the party that controlled Mexican politics for some 70 years. The Governor of Oaxaca, Ulises Ruiz, is a member of the P.R.I. and the teachers union has been trying to oust him through civil protests due to accusations of corruption and thier demands for higher pay.