Bloodstains on Leather: Examination of False Negatives in Presumptive Test and Human Hemoglobin Test

Presumptive tests for blood are very simple and sensitive tests used in the search for evidence. They also provide initial information on the nature of stains. A second test can confirm their nature. However, these tests can present false–negative results for different reasons. Some of those reasons have been studied, while others, those caused by the substrate material that contains the stain, are less well known. This work studies the effect of one component of a leather substrate—quebracho extract—on presumptive and human hemoglobin blood tests. Assays were performed using samples of blood dilutions contaminated with quebracho extract and others formed on a substrate containing the contaminant. Results show an undoubted interference that causes false negatives and even visible to the naked eye stains and also indicate that some tests (phenolphthalein) are more affected than others. Examiners should be taken into account when working on this kind of substrates.     

Identifying Irregularities in Mexican Local Elections

A generalized distrust in Mexican local elections raises the question of whether electoral corruption has vanished or remains a prevalent practice in the country. To answer this question, I analyze the 2010 gubernatorial elections, exploiting a feature of the country's electoral system: within each electoral precinct, voters are assigned to polling stations according to their childhood surname. Consequently, the only difference between voters in contiguous polling stations should be their last names. Given that political preferences are seldom correlated with voters' names, I use suspicious differences in turnout levels across contiguous polling stations to identify fraudulent practices. The findings of this article indicate that nondemocratic enclaves that actively obstruct the completion of Mexico's democratic transition still remain today.     

Chemistry in crime investigation: sodium percarbonate effects on bloodstains detection

Chemistry plays a leading role in crime investigation. In the study of bloodstains, chemical reactions provide the means for the detection. All these procedures have been thoroughly studied. However, recently, a new source of error has been found: washing stains with "active oxygen" detergents abrogates presumptive and human hemoglobin tests for bloodstains (although visible). The aim of this investigation was to evaluate the ability of pure sodium percarbonate-main component of detergents-to abrogate presumptive and human hemoglobin tests. Then, a solution to this problem could be found. The results demonstrate that pure sodium percarbonate-itself-is able to abrogate all tests, as well as the different degrees to which each of them is affected by the product. Consequently, faced with a stain of bloody appearance, even the preliminary tests are negative; it is advisable to analyze the DNA. Otherwise, the opportunity of obtaining valuable information is lost.     

Congress and the political expansion of the U.S. districts courts

Expanding the number of U.S. district judgeships is often justifiedas a response to expanding caseloads. Increasing judgeshipsduring unified government, however, allows Congress and thePresident to engage in political (patronage and ideological)control of the federal district courts. This paper examinesempirically the relative importance of caseload pressure andpolitical motives for Congress to expand the number of federaldistrict judgeships. We demonstrate that politics dominatesthe timing of judgeship expansion in the U.S. District Courts.We also show that both politics and caseload affect the actualsize of those timed expansions. In particular, we find thatbefore 1970, Congress seemed to have strong political motivationsfor the size of an expansion. After 1970, Congress became muchmore attentive to caseload considerations.     

Luminous lip-prints as criminal evidence

Luminescence is specially a useful property for the search of invisible evidences at the scene of a crime. In the latent fingerprints particular case, there are at one's disposal fluorescent reagents for their localization. The study of latent lip prints (that is lip prints from protective lipstick, or permanent or long-lasting lipstick that do not leave any visible marks) is more recent than fingerprints study. Because of the different composition of both types of prints, different reagents have been tried out on their developing. Although, lysochromes are particularly useful reagents to obtain latent lip prints, it may occur on coloured or multicoloured surfaces, the developing is not perceived due to contrast problems between the reagent and the surface where the print is searched. Again, luminescence offers the possibility to solve this problem. Nile Red is being studied as a potential developer for latent lip prints. The results on very old prints (over 1year) indicate that this reagent is highly efficient to get latent lip prints.     

Footnotes to Guamán Poma: Transtemporal Encounters in Nacha Vollenweider's Notas al pie

The graphic memoir Notas al pie (2017) written by Argentinian Nacha Vollenweider includes an illustration which reinterprets an image from the Nueva corónica y buen gobierno, a colonial document written by Quechua nobleman Felipe Guamán Poma de Ayala around 1615, when Peru was under Spanish rule. This article argues that if Guamán Poma's image portrays a critique of Western colonial power, Vollenweider's reappropriation follows its aftermath, and targets the structures of coloniality that underpin the formation of both individual and collective identity.