Of course, high profile crimes get disproportionate resources. In this case, they turned around a DNA test in a few days or less. The people involved, plus the submarine, assured this one gets attention.
As murders go this one has a lot of circumstances that facilitate solution in spite of all the attempts at muddying the waters.
I was more addressing the idea that you can't away with murder. Perhaps not in this case, but it obviously happens, and quite often.
If he was smart he would have driven his submarine to Russia and never come back.
And lack of clearance does not mean lack of guilt, more likely if there is no clearance it means that there is no case and most likely not murder.
You can use this as a proxy for the police 'solving' crimes but it would be much better to use the actual rate at which murderers are convicted because the police do not always get it right and do not always manage to establish guilt of the defendant beyond reasonable doubt.
I believe the UK is higher.
I'm an engineer and knowing that kind of forensic tools are available now to police, there is no way I'd ever think to commit such a crime (and also because WHY WOULD YOU DO THAT?!). Unless the police are very incompetent or you are able to conceal it very well, you will be caught. [0]
I can tell you I never had a class during my B.Eng about how to kill someone and destroy DNA evidence. I'm not sure what being an engineer has to do with sinking a dead body and removing DNA evidence, since these are not at all related to Engineering...
[0] https://en.wikipedia.org/wiki/Robert_Pickton