LE must have not only questioned him, but documented his physical condition at the time. I truly believe there was evidence of injury on him and blood evidence as well in the house. Who arrived first after the father called 911?
The link below has forensic case studies in addition to how assailants are wounded during a knife attack.
MECHANISMS FOR SELF-WOUNDING
During a violent attack with a knife or similar sharp instrument with its ensuing struggle, there may be numerous opportunities for the assailant also to sustain injuries.
By the very nature of such an assault, often with hand-to-hand combat and with multiple thrusts or slashes, it is quite difficult, or impossible, for the knife wielder to control each action. The following seven scenarios are proposed as possible causative factors in self-wounding.
Mechanism 1: While stabbing the victim, the assailant hits bone or otherwise resistant material. The abrupt stopping of the knife causes the assailant's hand to slide forward, allowing the hand gripping the knife to slide across the blade. Such a scenario typically would cause a slicing of the palmar surfaces of the hand or fingers. If the attack continues after the hand is cut, the presence of the assailant's blood on the knife handle reduces the gripping ability further, making even multiple self-wounding likely.
Mechanism 2: If the assailant wields the knife in one hand and tries to restrain the struggling victim with the other, it is possible that the assailant's hand on the victim will suffer a stab wound during the multiple thrusts. Such a stab wound would commonly be seen on the back of the hand or fingers or on the arm of the free hand.
Mechanism 3: If a folding knife without a locking blade, such as a jackknife, strikes a resistant surface, the knife blade can fold across the assailant's hand. Such an event would typically cause a guillotine-like knife-edge wound, either across the outer surfaces of the fingers or across the wrist or the heel of the palm, depending upon the knife's orientation in the assailant's hand.
Mechanism 4: Due to the great momentum involved in a typical stab, the knife may be capable of becoming lodged in bone or connective tissue. If the assailant attempts to remove the knife during the continuing struggle with the victim, it is possible that the hands could grasp a partially- exposed knife blade, causing slicing wounds to the palmar surfaces.
Mechanism 5: In a slashing action with a knife or other sharp-edged weapon, a glancing blow against the victim or a complete miss may, by the weapon's momentum, cause a slash injury to the assailant. Be cause of the virtually limitless degrees of freedom in how this slashing motion may be delivered toward the victim, the resulting injury to the assailant could occur to almost any part of the assailant's anatomy.
Mechanism 6: Similarly, defensive actions by the victim may cause a redirecting of the weapon's arc into the assailant. Again, the variety of possible movements makes for a limitless list of injuries possible.
Mechanism 7: In a struggle for control of the weapon, the assailant may grab for the weapon. This could result in slicing wounds to the palmar surfaces of the hand or fingers of the assailant.
