If you have a suspicion you should phone the police. The financial investigation team might look at it if they have other bits of intelligence or if they had an unproven suspicion at the time. However as you have put it on the Internet, contacting the police might not be wise.
If he’s bought property the normal SAR (suspicious activity report) process will have been followed and referred to the police if its unexplained.
Chances are he’s just saved up for years and finally thought he should spend it after a near death experience. Money in muck and all that.
My ten pence, legit scrap yards don’t get targetted by armed robbers unless they have loads of cash on site. New laws mean payments to banks after ID has been used to set up an account so they don’t do cash now.
It’s possible they were going to steal raw materials but scrapyards usually have great security, cctv etc. There are easier targets out there.
So, he either slept with someone he shouldn’t have, has cash on site for some unknown reason or he has been involved in dodgy dealings and brought it on himself, has terrible security or the other scrap yard wanted to put him out if business ?