Now it has been 40 plus years for me but what I remember is overlapping hard plastic pieces sort of like scales as the protection.The later jackets had pockets to stick plates in.
The damned collars used to interfere with your steel pot at the back of your neck when you tilted your head up.
I still think that the old jackets will stop most handgun rounds but I bet that our genius subject did not snap his vest closed. It was oh dark thirty and he likely was floating drunk. Take a look at the Daily Mail photos of you have not already done so.
Yeah, stupidity and incompetence all around!
I, however, do not believe criminal charges are warranted.
And, if I were on the jury, I'd hang it and hold a presser afterward and gloat at having wasted the taxpayers' money on the trial.