3 Source: SKH Lam Woo Memorial Sec. School CSI Case study (2010)
4 Footprint – the trace everyone left YouTube - Leave No Trace - Footprint EvidenceYouTube - Leave No Trace - Footprint Evidence (http://www.youtube.com/watch?v=qlmZZoL GMpM)http://www.youtube.com/watch?v=qlmZZoL GMpM
5 Important features in footprints important featuressignificance e.g. Size of footprint Real size of suspect s foot approximate height of suspect 1 Shape of footprintSex of the suspect 2 Type and brand (e.g. hiking shoes) Suspect s hobbies 3 Depth of footprint on soft material Weight of suspect 4 wear patterns and specific damages Walking habit of suspect 5 trace materials, such as soil, tar, rocks, and paint Places where suspect had visited
7 Taking photo of a footwear impression a1a1 a2a2 Case 1 Case 2
8 Taking photo of a footwear impression The ratio in case 2 is very close to that of the real shoe while a significant discrepancy appears in case 1. Case 1 is a wrong method since any angle other than 90 o in taking the photo will cause distortion of the image. The size and shape of the shoe may be misinterpreted. Correct Incorrect
10 Methods used in collecting footwear impressions (1) Electrostatic lifting
11 Methods used in collecting footwear impressions (1) Electrostatic lifting
12 Methods used in collecting footwear impressions (2) Casting
13 Individual characteristics on a footprint Figure 1 Figure 2
14 Number of Characteristics Probability of Occurrence p 11 / 80 21 / 3 200 31 / 85 333 Probability = Number of Characteristics Probability of Occurrence 11 / 10 000 21 / 50 000 000 31 / 166 666 666 667
15 Individual characteristics on a footprint It is highly unlikely that two different shoes would share all the same identifying characteristics. If 2 -3 characteristics share between the footprint in a crime scene and the suspects shoe, it would be a strong evidence that the suspect had been to the crime scene. Otherwise, this may eliminate the suspect as having been there.
16 Want to knows more ? In probability theory, to say that two events are independent means that the occurrence of one event makes it neither more nor less probable that the other occurs.probability theoryevents For example: The event of getting a 6 the first time a die is rolled and the event of getting a 6 the second time are independent. If two cards are drawn with replacement from a deck of cards, the event of drawing a red card on the first trial and that of drawing a red card on the second trial are independent.
17 Measurement of human gait at crime scene: Sex, height of the thief, direction of movement, walking or running, special walking habit, carrying load or not, drunken or under medication (if the gait shows instability)
19 Measurement of human gait at crime scene : (1) If footprints are deep and the pace is long, rapid movement is apparent. Long strides and deep prints with toe prints deeper than heel prints indicate running (A) (2) Prints that are deep, short, and widely spaced, with signs of scuffing or shuffling indicate the person is carrying a heavy load (B). (3) Persons walking backward (C) have a short, irregular stride. The prints have an unnaturally deep toe, and soil is displaced in the direction of movement. (4) To determine the sex (D,E), we should study the size and position of the footprints. Women tend to be pigeon-toed, while men walk with their feet straight ahead or pointed slightly to the outside. Prints left by women are usually smaller and the stride is usually shorter than prints left by men.