Forensics/Analysis

This unit focuses on the analysis of the handwriting features and human audio in FBI cases. The research is aimed at revealing the peculiarities of this material in the forensics area from the point of view of the Federal Bureau of Investigation but in a simpler way to get a general idea how this institution works. The objective is to define the principles features in a forensic analysis.

Praat spectogram standard settings

Table of contents

Introduction

1. Overview

The handwriting analysis aims to the analytical study of graphic design and the elements that surround it, (paper support and item writer) to establish with absolute certainty the authenticity or falsity of a document, trying at the same time to identify the author or authors. The man does not have the perfection of a machine to repeat the same movements. Spontaneous of the same author writing will show a logical change in its characteristics, within a certain range, higher or lower according to the individuals. Meanwhile, the audio recording is today a widespread practice , frequent and easy to perform for any citizen. Any user of mobile telephony, pda´s, and personal computer, can make their own recordings, store them and edit them if it is necessary. Audio samples can be accepted by the courts in all kinds of trials (labour, criminal and civil), provided the person who recorded part of the conversation. In this aspect, the constitutional law understands that the recording by one of the partners in the conversation is not a violation of the secrecy of communications, and does not violate the right to privacy. Solutions that need to be addressed from the acoustic forensic creating procedures and tools that ensure the capture, custody and the analysis of the stored data.

Before an analysis of handwriting

According to the science of graphology , the handwriting analysis is based on the intrinsic and extrinsic analysis. Where the first covers the examination of the general appearance of writing, i.e., the study of the generic features that undoubtedly make the graphic personality of the scribe, comprising a number of factors that must be thoroughly analyzed separately, and are: SPONTANEITY, rhythm of writing (speed, hold the item writer, thick strokes and features, continuity), tilt axis of writing DIAGRAMMING, GAUGE STROKES AND TRAITS, IRRADIATION AND GRAPHIC CULTURE. While the intrinsic encompasses the study of the peculiar details or automation of the clerk, which in sufficient quality and quantity will allow the Scriptural graphic identity, including the study of: the SPONTANEITY, strokes and features, links, MORPHOLOGY, punctuation signs, the spelling and the dimensions of literature.

So, the process of analysis of the letter when comparing two documents - one by a well-known author, one by a unknown author - does not start with checking for similarities, that any of us could do with a good degree of accuracy, but instead studied with verification of differences. Differences that initially to determine if it is possible that the same person wrote two texts once they are collated. If there are enough individual features key differences, and these differences do not appear to be the result of the simulation (an attempt to disguise own writing by hand or copy someone else's), then, the two documents were not written by the same person.

1. The basic features of handwriting
2. The basic analysis
3. Glossary of graphology

Before an analysis of human voice

The goal of the recognition automatic speech (RAH) is to imitate the process of recognition which takes place the receiver in the comunication. There are several levels of recognition in a human process, and different automatic recognition systems implement all-some or only the most basic depending on what is it application and complexity.

Secure data removal

We must proceed to capture secure data for further treatment and analysis. The devices extract all information from a mobile device (address book, record calls, voice, pictures, text messages, etc.).

LPC (Linear Predictive Coding) analysis

The LPC analysis focuses as a process of separation between the fine structure of the spectrum (harmonic frequency distribution) and the spectral envelope (formed by the peaks corresponding to each element of the signal).

Histogram

Graphical representation of the fundamental frequency (F0) of the audio signal, its average value and the corresponding deviation. Statistical values also provide us with the percentage of time with voice and non-voice, and the intensity of the signal.

Ic-1a-original-histogram

Double FFT analysis and transfer function

Through a mathematical calculation we can relate and compare 2 audio signals to establish similarities or differences in the domain of the frequency, amplitude and time. Very reliable procedure for locating small fragments, phrases or words that have been cut or replaced by others.

Double FFT analysis and transfer function

With the help of special teams, the investigated voices, which are already acquired across interceptions of calls or common recordings. They are submitted to analyses that allow us to identify the characteristics of the voice, with the end to find a supposed culprit. Every day, the experts in "Forensic acoustics" take as a study object recordings of supposed extortionists, kidnappers, terrorists, etc. The analysis of voices that is realized in this area, (with judicial previous order) begins with the exact transcription of the dialogue contained in the tape. Some peculiarities like the elimination of phonemes, regional words, between others, must be born in mind by the forensic audio laboratory at the moment of the transcription of the tape. The transcriptions must be exact and the tape cleanliness in order to individualize the voice, because the morphologic characteristics of system of phonation are only in the human being. The dialogue is studied analyzed in different perspectives such as linguistically, semantically and grammatically , what verbs it uses and how it uses them, if it omits phonemes. With judicial previous order, the cassettes are submitted to studies to determine how there is the original sound of each of the vowels and consonants since they go out of the vocal cords. So, changing the accent, having flu, speaking slowly or more rapid is not inconvenient to identify a supposed culprit.

1. The basic features of human voice
2. Example 2

Audiovisual material

• Tim Grant on Forensic Linguistics

Articles, papers and presentation

• A Definition of Forensic Linguistics
• "The linguist as expert witness" by Malcolm Coulthard
• “Some Forensic Applications of Descriptive Linguistics” by Malcolm Coulthard
• "Rape as Social Activity: an Application of Investigative Linguistics" by Tim Grant and Jessica Woodhams
• "What is Language and Law? And Does Anyone Care?" A paper by Peter Tiersma of Loyola Law School (pdf file)
• ‘The discursive construction of evidence in police interviews: case study of a rape suspect’ by Kate Haworth

See also

Key words: human voice, handwriting, analaysis, semantics, biometro, histogram, spectogram.