Bloomberg reported that while the amount of capital at the six largest U.S. lenders has almost doubled since 2008, policy makers and some Wall Street veterans say that’s not enough. They see a system still too leveraged, complicated and interconnected to withstand a panic, and regulators ill-equipped to head one off — the same conditions that led to the last crisis.

Bloomberg notes that the biggest risks could lie in the unknown: Five years after AIG was brought down by billions of dollars of credit-default swaps, there’s little transparency about banks’ trading and derivatives businesses or their counterparties.

Bloomberg said realizing that Dodd-Frank and new international capital rules haven’t made the system safe enough or kept banks from being too big to fail, U.S. regulators are pushing for tougher standards.

Bloomberg quotes an economics professor at the University of Chicago as saying, “The basic model hasn’t changed much, and it’s still fragile – the banks need much more capital and liquidity. They’re still way short of being safe.”