allegations of bitcoin being used for untraceable money laundering

Or perhaps another angle to try to suss out the heart of the issue would be to compare any scenario you might think of, to an alternate using physical gold, instead of bitcoins. Sure, there may be increased shipping fees, but lets presume that is not a burdensome enough overhead to worry about, as the real optimization targeted is ability to not to have a greater chance of being arrested for the moneylaundering and/or other crimes.

I.e. what is it about the gold version of the scenario, compared to bitcoin, that makes it easier for the authorities to catch the bad guys?