When in October 2021 Mexican president Andrés Manuel López Obrador issued a decree setting up a truth commission to explore state human rights abuses from 1965 to 1990, the reception was mixed. The president's backers celebrated it as a final opportunity to shed light on a dark era. Critics asked why López Obrador had not issued the edict until halfway through his term. And some feared that history might be repeating itself, for 20 years earlier President Vicente Fox had created a special prosecutor's office, the Fiscalía Especial para Movimientos Sociales y Políticos del Pasado, to investigate forced disappearances during the “dirty war” of the 1970s and 1980s. After five years of work, the special prosecutor's office delivered a total of zero convictions, effectively prolonging Mexico's history of impunity. How and why that happened is the subject of the important and original study Policing the Past.Javier Treviño-Rangel is a sociologist, but his book is almost as much a work of history. His sources include secret service documents from the national archive and the papers of the late human rights activist Adolfo Aguilar Zínser. His scope is not only the Fox years (2000–2006) but also the seven-decade “perfect dictatorship” that preceded it. After introducing the concept of transitional justice—the ways by which democratizing countries hold former state actors to account for crimes against the population—the author surveys repression of dissent under the Institutional Revolutionary Party (PRI), whose rule he terms “authoritarian” (p. 23). Most historians today prefer “semiauthoritarian,” but Treviño argues the era was characterized by a multifaceted “repressive machine” (p. 23), and seeing all of that machine's cogs and levers bared in a single chapter gave this historian pause: perhaps our discipline has overargued that PRI rule was more dictablanda than dictadura. On the other hand, the PRI was not as monolithic, nor was its “machine” as efficient, as the author implies.The tour begins with the “social dissolution” law and creation of sinister intelligence service the Federal Security Directorate in the 1940s. It proceeds through episodes of social protest and dissidence that met with ironfisted suppression: the railroad workers' strike of 1959, the opposition movement of Salvador Nava in early 1960s San Luis Potosí, the 1965 doctors' movement in Mexico City, the student movement of 1968, the dirty war against leftist groups, and the early years of the left-wing Party of the Democratic Revolution, more than 400 of whose members were allegedly killed under President Carlos Salinas de Gortari (1988–94). In his inaugural speech in December 2000, Fox promised that his regime would protect and respect human rights “like never before” and that there would be “no pious oblivion for those who committed crimes” (pp. 55–56).Eleven months later, Fox appointed the special prosecutor's office—as a dependency of the attorney general's office—at the recommendation of the semiautonomous National Human Rights Commission (CNDH). In Treviño's telling, the special prosecutor's office was set up to fail. The CNDH's role was key because it had spent the previous decade doing little to solve Mexico's biggest lingering human rights issue: forced disappearances. It was thus a performative body whose institutional instincts were to perpetuate impunity, at least within the establishment. The second key player to sabotage transitional justice was the PRI. Since Fox's National Action Party lacked control of congress, it needed opposition votes to pass legislation, and this gave it a strong disincentive to prosecute PRI members. Treviño claims that Fox feared “instability”; gridlock is more accurate, but the wider point is taken (p. 161). The third key player was the army, which refused to cooperate. At one point it tried three officers identified by the special prosecutor's office as coresponsible for the disappearance of 143 people, but the trio had already been jailed for drug trafficking, and the military tribunal anyway acquitted them. Finally, the attorney general's office itself was apparently an obstacle, headed as it was by a general once subordinate to an infamous head of the secret police.Institutional hindrances were compounded by legalistic ones. “Forced disappearances” are hard to prosecute as many actors may be involved in what is often a multistep process: arrest, incarceration, sometimes hospitalization, sometimes torture. There were statute of limitations issues. Altogether, in five years, the special prosecutor's office obtained warrants for just twelve former officials, of whom only six were arrested. None was convicted.Treviño could have infused his study with greater insight by interviewing senior officials of the Fox era, some of whom (foreign minister Jorge Castañeda and Fox himself, among others) are hardly press-shy. He should have discussed the evolution of the CNDH and the loyalties of those that headed it, for it was surely not the same institution in 2001 as it was in 1990, when created by Salinas. The book also suffers from lax editing: awkward translations; some acronyms rendered in English, others in Spanish; much repetition. However, Treviño offers a persuasive indictment of transitional justice a la mexicana, evidently less effective than its Argentine equivalent. Among other things, one hopes that it may serve as a cautionary tale to those seeking to clarify Mexico's past human rights abuses today.