The meaning of "things could slip through, heads could be turned, wheels greased"

[kjc0123]

What is the meaning of The meaning of "things could slip through, heads could be turned, wheels greased" in the following sentences?

 

Riding in a cab back to the airport, Ray did the math on his legal pad. For a judge like the one in Chicago, it would take eighteen years, stealing at the rate of a hundred seventy-five thousand a year, to accumulate three million. And that was Chicago, with a hundred courts and thousands of wealthy lawyers handling cases worth much more than the ones in north Mississippi. The judicial system there was an industry where things could slip through, heads could be turned, wheels greased. In Judge Atlee's world a handful of people did everything, and if money was offered or taken folks would know about it. Three million dollars could not be taken from the 25th Chancery District because there wasn't that much in the system to begin with. 

[jno]

This is a reference to corruption and bribery, though apparently on a small scale. slip through = be overlooked. Heads could be turned means people could be persuaded to look the other way while something illegal was going on. Wheels could be greased is a way of comparing money and grease: grease makes a wheel go round more quickly; if you pay someone money to overlook a flouting of the rules, what you are doing will proceed more quickly. 

[Peter Pedant]

he issaying that the judicial system is corruptible - in three different phrases - metaphors

lists of three have been used for emphasis in Western writing for around 2000 years, it is mentioned as a such in one of the Latin texts on rhetoric - Cicero I think