Well, so much for rational discussion, I guess.
Still: if you are contending (as it seems you are) that because some government officials have acted atrociously (which I deem an irrefutable and incontestable FACT), that it necessarily follows that we can never trust any government officials without implementing an assortment of institutionalized checks and balances, I am in PARTIAL agreement.
However, there comes a point where you have to acknowledge that a rogue government agency bent of doing something Orwellian (as you have envisioned) could accomplish it without the checks and balances you want to put up in either of two ways: (1) they could simply ignore the checks and balances, DO the nefarious acts, then lie their asses off and cover up (on the theory that if you're gonna commit official murder, you aren't likely to be overly concerned with coverups and lying) or (2) they could present falsified "intel" to "justify" their conduct in advance (thereby getting the official stamp of approval from the Congressional oversight committee or the courts as the case may be).
If we have officials in office willing to commit official murder without valid justification, then neither one of those two options seems all that difficult for them to also contemplate and accomplish.
So my question becomes: what actual purpose do the checks and balances
then serve? I KNOW what they are designed to achieve and would dearly love it if they could serve that purpose in all cases. But the POINT is: under my two scenarios, they don't serve that purpose at all
becausethe very officials you seek to pen in and hamper are lawless. And if they are lawless enough to seek to kill a person for invalid reasons, then they are very likely lawless enough to perjure themselves to get the prior stamp of approval if that's what they must do to achieve their illegal agenda.