Invalid Forensic Science Testimony and Wrongful Convictions

This is the first study to explore the forensic science testimony by prosecution experts in the trials of innocent persons, all convicted of serious crimes, who were later exonerated by post-conviction DNA testing. Trial transcripts were sought for all 156 exonerees identified as having trial testimony by forensic analysts, of which 137 were located and reviewed. These trials most commonly included testimony concerning serological analysis and microscopic hair comparison, but some included bite mark, shoe print, soil, fiber, and fingerprint comparisons, and several included DNA testing. This study found that in the bulk of these trials of innocent defendants - 82 cases or 60% - forensic analysts called by the prosecution provided invalid testimony at trial - that is, testimony with conclusions misstating empirical data or wholly unsupported by empirical data. This was not the testimony of a mere handful of analysts: this set of trials included invalid testimony by 72 forensic analysts called by the prosecution and employed by 52 laboratories, practices, or hospitals from 25 states. Unfortunately, the adversarial process largely failed to police this invalid testimony. Defense counsel rarely cross-examined analysts concerning invalid testimony and rarely obtained experts of their own. In the few cases in which invalid forensic science was challenged, judges seldom provided relief. This evidence supports efforts to create scientific oversight mechanisms for reviewing forensic testimony and to develop clear scientific standards for written reports and testimony. The scientific community can through an official government entity promulgate standards to ensure the valid presentation of forensic science in criminal cases and thus the integrity and fairness of the criminal process

Invalid Forensic Science Testimony and Wrongful Convictions

This is the first study to explore the forensic science testimony by prosecution experts in the trials of innocent persons, all convicted of serious crimes, who were later exonerated by post-conviction DNA testing. Trial transcripts were sought for all 156 exonerees identified as having trial testimony by forensic analysts, of which 137 were located and reviewed. These trials most commonly included testimony concerning serological analysis and microscopic hair comparison, but some included bite mark, shoe print, soil, fiber, and fingerprint comparisons, and several included DNA testing. This study found that in the bulk of these trials of innocent defendants - 82 cases or 60% - forensic analysts called by the prosecution provided invalid testimony at trial - that is, testimony with conclusions misstating empirical data or wholly unsupported by empirical data. This was not the testimony of a mere handful of analysts: this set of trials included invalid testimony by 72 forensic analysts called by the prosecution and employed by 52 laboratories, practices, or hospitals from 25 states. Unfortunately, the adversarial process largely failed to police this invalid testimony. Defense counsel rarely cross-examined analysts concerning invalid testimony and rarely obtained experts of their own. In the few cases in which invalid forensic science was challenged, judges seldom provided relief. This evidence supports efforts to create scientific oversight mechanisms for reviewing forensic testimony and to develop clear scientific standards for written reports and testimony. The scientific community can through an official government entity promulgate standards to ensure the valid presentation of forensic science in criminal cases and thus the integrity and fairness of the criminal process

The effect of forcing on the spatial structure and spectra of chaotically advected passive scalars

The stationary distribution of passive tracers chaotically advected by a two-dimensional large-scale flow is investigated. The tracer field is force by resetting the value of the tracer in certain localised regions. This problem is mathematically equivalent to advection in open flows and results in a fractal tracer structure. The spectral exponent of the tracer field is different from that for a passive tracer with the usual additive forcing (the so called Batchelor spectrum) and is related to the fractal dimension of the set of points that have never visited the forcing regions. We illustrate this behaviour by considering a time-periodic flow whose effect is equivalent to a simple two-dimensional area-preserving map. We also show that similar structure in the tracer field is found when the flow is aperiodic in time.Comment: 7 pages, 9 figure

The chemistry of fluorine-bearing molecules in diffuse and dense interstellar gas clouds

We present a theoretical investigation of the chemistry of fluorine-bearing molecules in diffuse and dense interstellar gas clouds. The chemistry of interstellar fluorine is qualitatively different from that of any other element, because - unlike the neutral atoms of any other element found in diffuse or dense molecular clouds - atomic fluorine undergoes an exothermic reaction with molecular hydrogen. Over a wide range of conditions attained within interstellar gas clouds, the product of that reaction - hydrogen fluoride - is predicted to be the dominant gas-phase reservoir of interstellar fluorine nuclei. Our model predicts HF column densities ~ 1.E+13 cm-2 in dark clouds and column densities as large as 1.E-11 cm-2 in diffuse interstellar gas clouds with total visual extinctions as small as 0.1 mag. Such diffuse clouds will be detectable by means of absorption line spectroscopy of the J = 1 - 0 transition at 243.2 micron using the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Herschel Space Observatory (HSO). The CF+ ion is predicted to be the second most abundant fluorine-bearing molecule, with typical column densities a factor ~ 100 below those of HF; with its lowest two rotational transitions in the millimeter-wave spectral region, CF+ may be detectable from ground-based observatories. HF absorption in quasar spectra is a potential probe of molecular gas at high redshift, providing a possible bridge between the UV/optical observations capable of probing H2 in low column density systems and the radio/millimeter-wavelength observations that probe intervening molecular clouds of high extinction and large molecular fraction; at redshifts beyond ~ 0.3, HF is potentially detectable from ground-based submillimeter observatories in several atmospheric transmission windows.Comment: 34 pages, including 11 figures (10 color), accepted for publication in Ap

Chaotic mixing induced transitions in reaction-diffusion systems

We study the evolution of a localized perturbation in a chemical system with multiple homogeneous steady states, in the presence of stirring by a fluid flow. Two distinct regimes are found as the rate of stirring is varied relative to the rate of the chemical reaction. When the stirring is fast localized perturbations decay towards a spatially homogeneous state. When the stirring is slow (or fast reaction) localized perturbations propagate by advection in form of a filament with a roughly constant width and exponentially increasing length. The width of the filament depends on the stirring rate and reaction rate but is independent of the initial perturbation. We investigate this problem numerically in both closed and open flow systems and explain the results using a one-dimensional "mean-strain" model for the transverse profile of the filament that captures the interplay between the propagation of the reaction-diffusion front and the stretching due to chaotic advection.Comment: to appear in Chaos, special issue on Chaotic Flo