In the literature, a few suicides by ligature strangulation and/or hanging inside a car have been reported. Vehicles are generally unsuitable for hanging or ligature strangulation because they are narrow in space. There is no room enough to suspend the body from a rope or to secure the rope to a rigid support [23]. All the hanging deaths reported in the literature review occurred in vehicles off, and none were related to decapitation. This is surprising since in judicial hangings, death is commonly caused by fracture-dislocation of the upper cervical vertebrae with transection of the cord, and decapitation can occur if the victim falls too far from the gallows [24]. If the victim falls an insufficient distance, strangulation can occur rather than breaking the neck. Instead, this comprehensive review shows that decapitation occurred only in 7 cases but classified as ligature strangulation due to the acceleration forces of the vehicles in motion. In ligature strangulation, the forward motion of the vehicle must be considered the external physical force acting on the neck through a tightened ligature [16, 25]. In hanging, the victim’s own body weight exerts compressive forces on the neck by a ligature, such as the vehicle’s seat belt, a rope, or clothing belt. All hanging cases are reported as atypical, unusual, and incomplete based on the body position and the configuration of the ligature marks. All ligature marks were represented by a single oblique furrow that encircled incompletely the neck, except for the seven cases with clear-cut decapitation. In two hanging (cases #4 and #17), and in three ligature strangulation (cases #6, #11, #14) the furrow completely encircled the neck. In the other three ligature strangulation, the furrow was incompletely encircling the neck (cases #1, #13, #15), as well as in 5 hanging cases where the ligature mark was oblique and superficial as near the knot (cases #2, #3, #5, #12, #16).

In ligature strangulation, decapitation requires a fast acceleration of the vehicle in motion and the use of an inelastic ligature [26], such as a cable steel or a nylon twisted rope. Vehicle-assisted self-strangulations can lead to decapitation when a ligature is pulled between the victim’s neck and a stationary object outside the car as the anchor of the ligature and the driver starts the vehicle [20]. These cases remain relatively uncommon and require careful investigation and analysis of the death scene to rule out other causes and manner of death. In cases where the vehicle is off and its force isn’t acting as an external force on the neck, differentiating between hanging and ligature strangulation can be a complex task because of the challenge in identifying the underlying mechanism of death (airway obstruction, vascular occlusion of the main arteries and veins, and carotid sinus reflex). This is especially true in cases where no common signs of asphyxia are found at external and internal examination such as in the additional case study reported by the Authors.

In the forensic literature, the classification of asphyxia is not uniform between authors, and similar cases can be assessed differently by forensic pathologists. According to a classification of asphyxia proposed by Sauvageau and Boghossian [27, 28], three different types of strangulation based on the source of the external pressure on the neck can be determined: hanging involves a constricting band tightened by the body’s gravitational force; ligature strangulation involves a force other than the body weight contributing to asphyxiation; manual strangulation entails pressure applied to the neck by hands, forearms, or other limbs. Nevertheless, the authors recommend labeling all asphyxia deaths from external compression to the neck as strangulation. If a specific subtype (manual, ligature, or hanging) cannot be determined, it should be classified as ‘strangulation nos’ (not otherwise specified) [27].

In a recent review, the definition of suicidal ligature strangulation has been expanded to include cases involving the attachment of the ligature to additional weights or devices to sustain the compression to the neck [29]. This recommendation can be applied to the self-garroting case #13, where the victim used a metal stick to tighten the rope around the neck, and to the additional case example observed by the Authors. In our case, no signs of asphyxia were found, except for a broad pale furrow due to soft noose and some conjunctival petechiae at the right eye only. No other hemorrhages were present at external or internal examination. This is not surprising. It is known that in asphyxia victims due to compression of the neck using a ligature postmortem findings on external and internal examination may vary considerably depending on the type of violent neck trauma, the intensity with which a victim resisted, as well as the intensity and duration of neck compression [25].

Some authors [24] report that in more than half of the hanging cases, there are no injuries on internal examination of the neck structures and hemorrhages in the neck muscles are often absent [25]. The likelihood of fractures in the laryngeal and hyoid structures varies according to the degree of ossification and depending on age [25]. At external examination, a recognizable, distinct, and well-demarcated furrow was described only in 13 out of 20 cases in total. In the other 3 cases (2 hanging and 1 ligature strangulation), the furrow was poorly defined and pale, devoid of bruises and abrasions at the upper or lower margins, although the ligatures were mostly hard (i.e., electrical cord, rope) except in case #17, in which a shoelace was used [8]. These findings can exhibit significant variability, predominantly influenced by the material used as ligature, its characteristics, and texture. If the ligature is a soft material, such as a towel, the groove might be faint and pale, indistinct, barely visible, poorly defined [30].

In a comparison of post-mortem findings observed in homicidal and suicidal ligature strangulation [31], bleedings in the neck muscles seldom occurred in suicides. However, the laryngo-hyoid injuries could be helpful in the differentiating suicides from homicides if more than a single thyroid horn fracture or a laryngeal soft tissue trauma is present. In a revision of 116 cases, of suicidal ligature strangulation the number of laryngo-hyoid fractures and hemorrhages was generally low and extremely uncommon [32], probably due to the severe compression of the blood vessels brought about by strangulation [17].

In this comprehensive review, facial congestion and petechiae (conjunctival or at eyelids) were reported only in 9 out of 20 cases in total, among which 7 out of 11 cases of ligature strangulation (with/without decapitation) and only 2 hanging. According to Di Maio and Di Maio [24] petechiae of the conjunctivae can be mostly observed in ligature strangulation cases compared to hanging cases, because, unlike in hanging, there is no complete occlusion of the vessels and blood continues to go into the head from the vertebral arteries. Tongue hemorrhages were also mostly observed in ligature strangulation (3 cases) and in one hanging victim. In ligature strangulation, hemorrhages can mostly occur at the tongue due to the anatomical vicinity of the jugular and carotid vessels and congestion of the face and neck with increased intravascular cephalic venous pressure [33]. Hemorrhages in the soft tissues and muscles of the neck were again found mostly in ligature strangulation with decapitation (7 cases), along with thyroid cartilage fractures and one fracture of the hyoid bone.

Unfortunately, no internal signs often associated to hanging like the Amussat’s, Friedberg’s, or Brouardel’s signs, were reported. Petechial hemorrhages spots on pleural or epicardial surfaces were only reported in 2 cases of hanging and one ligature strangulation.

In two hanging cases and in the additional case reported by the Authors, no internal findings of asphyxia were found. The lack of internal sings of asphyxia can be explained in these cases by the combination of the three main mechanisms involved in death following the compression to the neck (airway obstruction, vascular occlusion of main arteries and veins, carotid sinus reflex). These mechanisms can act independently or in combination. For example, when the role of the carotid sinus reflex is prevalent, both external and internal findings in the form of local hemorrhages may be easily absent due to the rapid death. The vagal reflex mechanism can be a poor contributing factor in the case of hanging, as cerebral ischemia is primarily caused by the compression of the arteries with no distinct related injuries or hemorrhages of the neck.

Indeed, determining the type of asphyxia death (ligature strangulation or hanging) for victims who died due to compression to the neck by a ligature can be challenging [34, 35]. This is also due to the misconception that strong pressure is needed on the neck to occlude the airways and the arterial vessels of the neck. It has been demonstrated that a force of 8–12 kg is necessary to occlude the airways [36], whereas a lower amount of pressure is enough to occlude the carotid arteries and veins but not the vertebral arteries that need a load of 30 kg approximately [37].

Therefore, the weight of the head against a noose can be sufficient to occlude the carotid arteries and cause death [24]. In this context, the carotid sinus reflex can be triggered both by a minimal pressure to the neck, at the level of carotid artery bifurcation, or by longitudinal stretching of the carotid artery [36]. The hypothesis of manual compression triggering the carotid sinus reflex and fatal cardiac arrhythmias has been also suggested as a mechanism of death [38]. An individual with minimal autoerotic experience by ligature may unintentionally suffer immediate syncope or coma by carotid sinus pressure [36]. The hypothesis of an accidental autoerotic death was raised by the Authors in case #6 [12] and considered in our case report due to the left hand found close to the paint zip open. This hypothesis was discarded soon after the discovery of a suicidal note inside the car.

The accidental autoerotic death by ligature is commonly the consequence of the failure of a release mechanism after using hypoxia to enhance the sexual response while masturbating [39, 40]. The individuals choose hanging or ligature strangulation to obtain compression of the carotid arteries and stimulation of the carotid sinus reflex to produce an orgasm-enhancing effect. Usually, autoerotic asphyxia is performed in indoor settings (victim’s own home) [36] but, sometimes, bodies could be found in public areas (open fields but also cars) [41]. The exposure of the genitals, a complete or partial nudity, the presence of pornographic material on the scene, and the victim’s hands near the genitals could suggest antemortem sexual activity [42, 43]. The presence of semen does not necessarily indicate evidence of antemortem masturbation since ejaculation may occur because of neurophysiological reflexes [44, 45].

Therefore, the discrepancies between external and internal findings and the suicidal or accidental asphyxia deaths by ligature strangulation and/or hanging are not surprising. A comparative study of the pathological features found in ligature strangulation, suicidal hanging, and autoerotic deaths shows that internal injuries are uncommon in suicidal hanging and in autoerotic asphyxia [36]. In both cases, the severe compression of the blood vessels as well as the carotid sinus reflex can easily determine the absence of hemorrhages at the neck muscles and even around laryngeal and hyoid fractures. Although recommended by several Authors for the assessment of the vitality, immunohistochemical analysis of the ligature mark has not found yet general agreement among the scientific community. Validation protocols to promote consistency and comparability among immunohistochemical markers and to improve their reliability in routine diagnostics of vital reaction are still needed [30, 46,47,48].

The transfer of information collected at the death scene among investigators and the forensic pathologists is crucial for the reconstruction of events preceding the death and to assess the correct manner of death. In our case, the homicidal hypothesis was excluded based on the record of the video surveillance camera available at parking area.