I'm not about pointing the finger of blame, but changing the future while we have the opportunity. Noted that the shoulder harness bar is in tact and the passenger seat shoulder harness are present but driver's position absent. Though we don't know if they were cut away by responders. 50 years of Auto seat belts,(Nylon) webbing does not generally fail but stretches quite a bit(my est. X10) to a final failure point. My point is those straps use "buckles" that the webbing threads through, webbing goes around the bar and back through the buckles. I believe if the webbing is threaded through the buckles incorrectly it looks "ok" BUT the webbing can pull out. Double Check that yours are threaded into their buckles correctly please! I feel sure your belt manufacturer will gladly provide exact/correct instructions!(IF they won't help, throw that 5#it away! I wouldn't trust them!) A minute checking could make a big difference. I am fairly sure those adjuster buckles must also be made of steel and contiguous(not slotted for easy installation! as used on child car seats whose adjuster buckle component is doing a very different secondary duty cycle.), I do not believe plastic is an approved materiel for that component. All very tragic, and there is not much left to us but to Honor his memory and try to be as safe as possible!