Nobody is above the law and everybody deserves a fair trial without any outside interference. If an individual is guilty then the evidence will speak for itself. If you tamper with the evidence to make the verdict go in the direction you want it to then you should be prosecuted for a crime because you are playing with someone's life and when you are in a position of power you need to have a certain level of responsibility.
What is surprising is that it is not already a felony. Tampering with evidence is enough to get an entire case thrown out, which is why it should be such a serious offense. Too many cases have been thrown out because the evidence was mishandled or tampered with and people have gone free.
It should already be standard practice to not tamper with evidence. That is a crime or I thought it was. If laws are not already on the books then yes they should definitely add laws making tampering with evidence a felony. I believe the laws now may be misdemeanors. The problem with the justice system is that there is a win at all cost mentality in some of the district attorney offices, rather than finding the correct perpetrators of crime.
It is a terrible and unethical act to tamper evidence that will be used in court. This is especially true for prosecutors, as they are directly involved with cases and stand to profit from such tampering. If the punishment for changing evidence is made serious throughout the US, prosecutors will likely do so at a lower rate.