The tape and cord may have been from the house and any remnant might have been discarded. But where? We are missing the tape end, the cord end, the stun gun, and maybe the headbash weapon.
If it was an intruder, he could have taken those things with him. If it was not an intruder, the headbash weapon might be somewhere inside, the stun gun might have been non-existant, and the tape and cord could have been thrown over the hedge.
Did they determine what caused the head injury? Surely forensics could have if it were something like the bathroom taps or edge of tub or the maglight. Does anyone know about that or has it been kept secret in the case file.
Did they really check the neighbourhood for small items like the tape and the cord? Perhaps they are sitting under a bush down the lane.