However, I would guess a lot of those are fairly easy cases with witnesses, motive/means/opportunity laid out fairly obviously by people committing crimes in passion, even people that turn themselves in, etc. I haven't been able to find any data on what the clearance/success rate is for premeditated murders - where people actually took their time and made it difficult for investigators.
I was being hypothetical. Murder is of course illegal. I believe planning one is also illegal. While I don't have daughters, I can understand how the father in this case was driven to these extreme measures. In other words, the prosecution would probably reject me as a juror in this kind of case after even just two minutes of selection/questioning.
True, but here is the dirty little secret of that statistic: the unsolved murders are always murders committed by strangers; often chance encounters during the commission of other crimes, wrong time/wrong place, etc.
That is why serial killers take so long to catch. They literally have to become so completely predictable to the profilers and the police that they are, in a sense, "known." And even then, they have to make a serious mistake, lose control or have themselves accidentally stumbled upon in flagrante delicto.
On the other hand, you cannot murder someone you know and get away with it. Those crimes are almost always solved.
I am sure if I had a 14 year old daughter and she was raped I have it in me to plan revenge also. I have a feeling that the numbers are even worse because of people convicted that are innocence.
A significant fraction of murders are (1) domestic murders in which the jealous/abusive husband/boyfriend/"partner" kills his wife/girlfriend/"partner" or vice versa, (2) bar fights and other arguments in which two people fight over nothing (a perceived insult to their mother, their sports team, their girlfriend, etc.) and it gets out of hand, (3) gang-related disputes over territory or drug transactions, or (4) robberies gone bad.
Most murders are not subtle - 68% of all murders and a much higher proportion of solved murders use firearms. When something goes "bang", people look, and they see who is holding the gun or running away with a gun. Premeditated murders are comparatively rare in solved cases, but it's hard to know what fraction of all murders are premeditated. What we know is that most solved cases are pretty obvious - with witnesses to the bar fight or to the domestic quarrel (almost 50% of solved cases), security camera footage of the robbery (15%) or drug deal (8%) and shooting, and similar strong hints (with another 20% of killers in solved cases well-known to the victim) right at the start of an investigation.
Police are very good at solving these sloppy murders, but not at all good at apparently motiveless murders. If no one knew a father had reason to kill a man he suspected of raping his daughter, and if the father was not seen picking up the rapist just before the disappearance, they would be hard pressed to solve the case.