Here's the interest rate since 1985 for Treasury bills on the secondary market (it's the market rate, after Fed money pumping distortions).
Here's the US dollar LIBOR rate for the same period.
As can be seen the LIBOR rate direction pretty much reflects market direction. There might be some inside gaming going on, but it has little to do with significant manipulation. especially relative to Federal Reserve activity which caused the overall volatility in BOTH the T-bill rate and the LIBOR rate.