Equality before the law doesn’t only apply within a courtroom. It’s a fundamental principle meaning that all people are equally entitled to the protection of the law, in its application and its enforcement.
You are essentially arguing that the murderer of a drug dealer is intrinsically more entitled to get away with his crime than the murderer of a pre-teen girl. That’s not equality before the law.
In other words, you want the police to prioritize murder investigations based on their opinions of the moral worth of the victims, as long as their opinions on the subject agree with yours.
If the police think your (hypothetical) son Joe Blow was a shady drug dealer and you agree with them, then you’re okay with the police deprioritizing the investigation of his murder. If the police think your (hypothetical) teenage daughter was a delinquent little floozy and you don’t agree with them, then you object to their deprioritizing the investigation of her murder, because you assume that their assessment is a “rushed capricious judgement”.
Can you see how potentially subjective and debatable this line of reasoning is? And how wasteful it would be to have to get everybody agreeing on the moral worth of a murder victim before the police could decide whether to investigate their murder?
In the long run, as I said, it’s better and more efficient for everybody if the baseline assumption is just “murder is murder”.
You sure did: equal protection under the law, including the equality of assuming that someone’s not more entitled to literally get away with murder because their victim happened to have a criminal conviction, is most definitely a human-rights issue.
And we as a society can express that value judgement by not electing those criminals to be mayor (or for that matter, President), by refusing to admit them into our social circles, by not hiring them to do their criminal activities, by not putting up statues to them, and by denying them all sorts of other forms of recognition of social value and esteem. And also, most importantly, by legally convicting and punishing them for their crimes, in accordance with the provisions of our criminal code.
But we should not express that value judgement by unequal application of the law, such as treating the murder of criminals as more allowable and less punishable than the murder of non-criminals.