Introduction

Blood is most commonly and frequently found at the crime scene and is the most important and useful physical evidence for the forensic investigators (Li et.al. 2011). This evidence is used for the DNA- profiling to authenticate the suspect’s identity and its pattern reveals the direction of spattering in order to reconstruct the crime. Blood pool can easily be collected, preserved and examined by the analyst but sometimes investigators encounters the dried blood stains also. These dried bloodstains have a great value when used for the determination of age so as to find out the relative time of the trauma or bleeding because this information may help the investigators to determine, whether the stain is related to a crime and also the approximate time when the crime was committed (Edelman et.al. 2012). The blood begins to dry whenever it’s exposed to the external environment and the time required by it is directly proportional to the size, volume, nature of the surface and the involvement of other factors. Under normal condition of temperature and humidity the small, lighter and thin bloodstain pattern on non-porous surfaces dries easily and doesn’t take much time (Within few minutes), while under same conditions, the greater size or large volume blood stains requires longer period of time to get dry. The drying of blood stains begins around the periphery and then proceeds towards the central portion. The flaking central portion and the intact periphery or the rim of dried blood stain produces a characteristic skeletonized bloodstain. Age estimation of blood stain provides valuable and significant information and therefore found to be one of the important application during crime scene investigation (Inoue et. al. 1992).

Ageing of blood can be determined on the basis of color changes with the passage of time. As Fresh blood usually bright red in color because of the presence of oxyhemoglobin, after few minutes of deposition it appears dark red to bluish brown color because of the conversion of Hemoglobin (Hb) to Met-hemoglobin (met-Hb) and ultimately after few hours it appears dark brown color due to presence of hemichrome. So oxidation of HbO2 results into the color change of blood which can be used for age determination of blood stain (Bremmer, 2012). This method is not reliable because we cannot find the accurate time of deposition as the result by visual analysis can vary person to person therefore to authenticate the results, different scientists developed different techniques to achieve the best results.

It is reported that, for more than 100 years many scientists used several methods and techniques for the determination of age from dried blood stain and they also proved that these methods are reliable and can be applicable for the forensic purposes (Li et.al. 2011). The various compounds present in a blood stain and depending of that there are numerous methods that have been established for this purpose, some of them are electron paramagnetic resonance spectroscopy, reflectance spectroscopy, atomic force microscopy, oxygen electrode, hyper spectral image analysis, electron spin resonance spectroscopy etc. (Inoue et. al. 1992).

The aim of this study is to summarize all the methods, techniques, time duration (up to which it provides correct result) and its reliability which is used by different scientist for the age determination of blood stains. This review study also evaluates the imprecision and unreliable results of many techniques and also covers the recent development and the future challenges and other factor that influences the result.