>>6498
Well, you just explained yourself shy serial killers are much harder to catch than plain murder like in that submarine. Almost all normal murders happen in a similar way. where you almost immediately have a suspect...
Serial killers kill without motive and they select random targets in random places making it impossible to suspect them or prove their guilt.
They do go for many years until they finally screw up something badly.

If you want to avoid getting caught you must take really good care to hide murder motive or provide some scapegoat. Otherwise, it is practically impossible to avoid being caught, at best you may try to hide evidence to make your guilt unprovable but you will still get under careful investigation and police will follow you for years. it may convince you of murder even if you did everything perfectly and there is no evidence at all.

The guy in the submarine did a pretty stupid thing. He could have said that she just drowned or something and nobody could prove his guilt. Drowning her with the submarine was most the stupid idea ever. There is no reason to convince him for unintentional manslaughter because criminal neglect has to be proven. If she just fell into the water and drowned there is no guilt. All he needs to do is to cook some decent explanation of what happened.