The Trustee of a fund has a fiduciary (VERY HIGH) duty of loyalty and avoidance of self-dealing.
BUT the Trustee is NOT a guarantor of the assets and if the assets were invested appropriately, and the stock market declines, need not make up the difference.
If the Trustee stole the assets, that's a crime. If the Trustee was merely careless, that's not a crime, but he or she or it may be civilly liable.
As for statutes of limitations. yes there are several that would be applicable, depending on what charge is involved, and some are longer, some shorter. It's not just the statute but WHEN the act complained of is measured from and that's something you need local counsel on.