Cutaneous wound metallic residues pattern analysis with SEM-EDX in a forensic case of overkill

Introduction

Murder caused by excessive force and injuries than those needed to kill ¹ is designated as overkill – beyond the murder. ² In such cases, corpses usually show different patterns of harm due to the use of point-and-edge weapons, firearms or different kinds of blunt objects.^2,3 Commonly, multiple wounds inflicted intra-vitam with brute force ⁴ are detected on different areas of the body. The assessment of such crimes requires evaluation of some key characteristics: number of wounds, their distribution and morphology, and identification of the weapon or weapons involved. ⁵ Moreover, post-mortem toxicological examinations frequently detect the presence of high levels of alcohol and/or toxic substances. ⁶ Some victims are more at risk of overkill, such as homosexuals, while serial killers, psychotics and heterosexual adults with a history of domestic violence are more likely to enact it.^1,7 The perpetrator is often in a romantic or sexual relationship ² with the victim. We present an overkill murder perpetrated on a Peruvian transsexual who was choked and stabbed in the face 11 times. Scanning electron microscopy with energy dispersion X-ray spectroscopy (SEM-EDX) performed on the skin of facial wounds provided proof that two different point-and-edge weapons had been used by detecting metallic micro-traces of heterogeneous composition. This finding and the autopsy that highlighted the use of two different methods to kill (mechanical asphyxia and sharp-force trauma) designated this murder as overkill.

The case

A 41-year-old phenotypically male Peruvian transsexual was found dead at his home with no signs of forced entry. The police were alerted by a neighbour who had heard screams and noises coming from the victim’s apartment. The body, dressed in women’s clothing (Figure 1(a)), was lying prone on the ground in a puddle of blood, and had 11 stabs to his face. No weapons were found at the crime scene. A judicial autopsy was performed at the Institute of Forensic Medicine of the University of Milan.

OPEN IN VIEWER

Figure 1.

View of the findings observed at the crime scene investigation and at the autopsy.

Materials and methods

At autopsy examination, samples of biological fluids were taken and swabs were performed for toxicological and genetic analysis as well as viscera fragments including skin samples of facial wounds for histological investigations being collected. This latter underwent post-fixative processing and the sections obtained were stained with Hematoxylin-Eosin and Goldner’s Masson trichrome staining. Since some facial wounds, in particular those at the right supraorbital area and at the left eyebrow, had different morphology (length, depth and appearance of the margins) (Figure 2), the suspicion that they may have been produced by means of two different point-and-edge weapons arose. Therefore, for each of the above-mentioned sites, skin samples were collected to be analysed with SEM-EDX. To avoid contaminating the skin samples with iatrogenic metal particles (deriving from the blades of the autopsy instrumentation), a ceramic knife (Kyocera Ishi Ba) was used. Moreover, a distal lesion-free skin sample (right thigh) having a negative control purpose was collected. Finally, the sampled facial skin lozenges were placed in absolute ethanol for 30 min before being analysed with the Cambridge Stereoscan 360 microscope and Consolle Link Isis Oxford.

OPEN IN VIEWER

Figure 2.

Skin facial wounds sampled to be analysed with SEM/EDX.

Results

Toxicological investigations were negative for both the blood alcohol content and substances of abuse. The genetic–forensic investigations were not authorised by the investigating magistrate and therefore not carried out. The histological examination of the skin wounds and of cervical soft tissues showed acute haemorrhagic infiltration occurred intra-vitam, with well-preserved red cells dissociating the connective fibres up to the subcutaneous adipose tissue; finally, dense bilateral endoalveolar haemorrhagic infiltration deriving from massive broncho-aspiration was observed (Figure 3). On the basis of autopsy and histological examinations, the cause of death was identified as mechanical asphyxia in a victim subjected to severe multiple facial lesions inflicted by a point-and-edge weapon.

OPEN IN VIEWER

Figure 3.

In (a), skin facial wound with finding of recent and vital haemorrhagic infiltration (H&E 200×); in (b), section of cervical skin with finding of deep vital haemorrhagic infiltration dissociating the connective fibres up to the subcutaneous adipose tissue (Goldner’s Masson trichrome staining 100×); in (c), panoramic photomicrograph of the right pulmonary base with massive presence of blood in alveoli (H&E 3×); in (d), abundant septal interstitial blood extravasations and internal submersion (H&E 200×).

The SEM-EDX analysis carried out on the skin lozenges detected exogenous metallic micro-traces, isolated or agglomerated, consisting mainly of iron and chromium (Fe–Cr); the sample taken from the right supraorbital area showed only iron (Fe) in the one collected from the left eyebrow region (Figure 4). Conversely, the distal control skin specimen, as expected, did not show any exogenous metallic micro-traces.

OPEN IN VIEWER

Figure 4.

At the top, multiple metallic micro-traces, irregular in shape and size, located in the context of the facial wound connective tissue, made up mainly of iron and chromium at the compositional analysis; at the bottom, metallic micro-particle composed of iron only, with traces of organic phosphate (of bone derivation), in the context of the connective tissue and in the presence of still well-preserved blood cells.

Discussion

SEM-EDX analysis is an increasingly important tool used to identify exogenous residues on different cadaveric substrates. It postulated that they may deposit on biological matrices by means of a transfer mechanism due to the contact with the weapon. In cases of sharp-force trauma, SEM-EDX investigations have been carried out on bone substrates^8–10 with considerable sensitivity identifying metallic micro-traces. On human skin samples, the recent application of SEM/EDX analysis^11,12 was very encouraging and specific. ¹¹ In fact, as the morphology of point-and-edge skin wounds can be multiple and insidious, ¹³ the morphological assessments are often not sufficient to link the wounds on a corpse to the weapon involved even when the weapon is at the crime scene and more so when it is not there. SEM-EDX analysis can be used to guide the subsequent investigations and allow the identification of the weapon involved, since it proved to be a sensitive technique in detecting exogenous micro-traces deriving from the weapon and means of wounding and killing. ¹¹

We presented a murder case of overkill where two different means were used: mechanical asphyxia and sharp-force trauma (11 penetrating facial wounds inflicted by two different point-and-edge weapons). The autopsy showed that the victim died from lethal asphyxia, evidenced by multi-fragmentation of superior horns of the thyroid cartilage and hyoid bone, alongside the haemorrhagic infiltration of the surrounding soft tissues. Asphyxiation was probably quicker to kill the victim than blood loss from the multiple cuts on the face which were inflicted in a peri-mortem phase, as demonstrated by the vitality of the skin margins. Without the murder weapon, and in order to correctly assess the number and type of weapons involved, a particular scientific approach was required. In addition to conventional investigations, we also resorted to the SEM-EDX analysis of skin lozenges sampled from macroscopically different facial wounds which played an essential role identifying heterogeneous, metallic micro-traces, consisting of only iron in one sample and iron and chromium in the other. This confirmed the initial suspicion that two different point-and-edge weapons were used. A breakthrough occurred when investigators questioned the victim’s ex-partner who was the main suspect and he confessed. He claimed he had acted from jealous rage prompted by yet another refusal of reconciliation. He confessed he had attacked his ex-partner at the height of a quarrel, choking him and at the same time slashing with two different knives which he had removed from the crime scene. In accordance with Italian legislation, he was sentenced to 30 years in prison on charges of murder aggravated by torture and cruelty.

In our case, the SEM-EDX technique proved to be decisive in detecting the presence of different metallic micro-traces in the context of skin wounds of victim of overkill. This report emphasises the value of the SEM-EDX analysis, confirms its applicability even on cadaveric skin and encourages its potential use in forensic practice, especially in complex cases such as the one presented.