This paper describes the involvement of our laboratory in a Western Australian \'cold-case\' investigation that spanned 24 years. The investigation was widely considered to be the largest in Australian history. During the investigative phase, our laboratory was tasked with the collection of trace evidence of all types in connection with a sexual assault and two homicides that were suspected to be related. Textile fibres represented the vast majority of trace evidence recovered. A much greater quantity of fibres (>10,800) was collected than would be typical for a routine case, as fibres of any colour or type were potentially of investigative value. The investigation was unprecedented in its scale, and presented numerous challenges in terms of evidence recovery, analysis, interpretation, reporting, and provision of testimony. A textile fibre microspectrophotometric (MSP) database was developed specifically for the interpretation of data in connection with the investigation. The database currently contains over 25,000 normalised and first derivative spectra of casework, validation and reference textile fibres. A fibre comparison strategy was devised, involving the identification of preliminary fibre groups on the basis of corresponding/similar MSP spectra, and verification of these groups via brightfield and fluorescence comparison microscopy. A potential link to an automotive source was identified for one of the homicide victims during the investigative phase. After identification of a suspect, a total of 98 fibres recovered from victims and from a seized motor vehicle were found to correspond in properties to six different fibre types from known textile sources in connection with the suspect. A highly publicised criminal trial was held, and textile fibre evidence provided a major contribution to the trial findings, in which the accused was found guilty of two homicides.

The fibre traces on a young victim found underwater were mostly single fibre traces besides small amounts of fibre collectives indistinguishable from his parents clothes (mainly wool). Most of those single fibre traces were blue-grey polyester fibres showing tiny differences among each other. They were unexpected according to known population fibre studies. One year after the victim\'s discovery experiments were conducted to evaluate the possible contamination with fibres from river water. A small amount of extraneous fibres were collected among which blue and grey-black cotton and man-made (mainly polyester) fibres. All man-made fibres were single fibre traces and small fibre collectives were only observed for cotton. These results confirmed the frequent occurrence of blue and grey-black cotton fibres as background, but also highlighted the possible contamination with single blue and grey-black man-made fibres from river water. No wool was found, strengthening the significance of the wool fibre collectives present on the victim.

Fiber evidence found on a suspect vehicle was the only useful trace to reconstruct the dynamics of the transportation of two corpses. Optical microscopy, UV-Vis microspectrophotometry and infrared analysis were employed to compare fibers recovered in the trunk of a car to those of the blankets composing the wrapping in which the victims had been hidden. A \"pseudo-1:1\" taping permitted to reconstruct the spatial distribution of the traces and to further strengthen the support to one of the hypotheses. The Likelihood Ratio (LR) was calculated, in order to quantify the support given by forensic evidence to the explanations proposed. A generalization of the Likelihood Ratio equation to cases analogous to this has been derived. Fibers were the only traces that helped in the corroboration of the crime scenario, being absent any DNA, fingerprints and ballistic evidence.