Blood spatter analysis. Bloodstain on a surface surrounded by scale bars. Bloodstain patterns are analysed to help investigators determine: the origin on the body, the weapon used and the number of blows, the relative position of the victim and assailant and the sequence of events. In impact patterns, the length and width of each drop is measured and the angle at which they struck the surface calculated. This indicates the direction the blood was travelling in and the speed at which it travelled. The convergence point of the drops indicates the location of the victim. The dense stain alignment in this pattern indicates that the site of impact on the victim was in close proximity with the surface. The black arrow indicates the area where a DNA swab would be taken.