Earlier quoted context omitted.
It's not a false claim, assuming the feds will keep such a key "secure" is not backed by evidence. Top secret materials are leaked all the time. Private keys from well secured systems are extracted from hacks. The FBI having such a key would make them a very profitable target for the various corps that specialize in hacking for hire. For example, NSO group. If the power doesn't exist, nobody can exploit it.
Do military cryptographic keys leak often? Do nuclear codes leak? The times highly valuable cryptographic keys leaked for various cryptocurrency exchanges it has generally if not always been due to gross negligence. Such a key would be highly sensitive and it would also require very little traffic to use. You would just need to send the secure system a KEM ( I don't doubt they could secure it. Can even split the key…
For many years, the code was 00000000.
https://arstechnica.com/tech-policy/2013/12/launch-code-for-...