The Securities Exchange Act of 1934 Section 9 prohibits manipulation of security prices. It states "(2) To effect, alone or with 1 or more other persons a series of transactions in any security other than a government security, ...or raising or depressing the price of such security for the purpose of inducing the purchase or sale of such security by others.
One of the main manipulators for the price of silver is shorting it. The vast amounts of shorting occurring drives the price down keeping it artificially low and putting vast profits in the shorters hands. The big banks are the ones leading this manipulation led by JP Morgan.
The price of silver should be driven by supply and demand, not speculation in the short market