This kind of interrogation is held at a police station.
They are recorded - a lot of countries outside the US actually require it be recorded and if it is not, the interview and anything said in it are simply inadmissible.
Even in the US, recording is standard practice for any meaningful felony. Unlike body worn cameras, it does not get magically lost, and when it does, the interview is generally not admitted, or a defense lawyer tears it to shreds if the detective tries to use his notes. While there are always cases of recordings "being lost" or whatever, the rate here is very low, compared to body worn cameras or anything else.
The case where they don't do recording is usually resource related.
There are around 20,000 law enforcement agencies in the US.
80% of them have less than 25 full time employees
15% of those have 1 full time employee.
While most still do recording, it might only be for major felonies or whatever because they don't have the manpower to have handle recording 24/7.
Given that, you won't achieve 100% compliance without something drastic (for example, funding and paying for 24/7 video recording in every department). Even there, at best you'll just end up with only the cases where software/hardware went wrong.
Note that i have no love for police (actually, much the opposite), but i'm also realistic - i'm not sure it's easy to solve the problem of having tons of small, low-budget police departments, be required to record.
(the UK, by comparison, has 43 regional law enforcement forces, and is down to 300 police stations or something like this)