US banking regulators swooped in to seize mortgage lender IndyMac Bancorp Inc on Friday after withdrawals by panicked depositors led to the third-largest banking failure in US history. California-based IndyMac, which specialized in a type of mortgage that often required minimal documents from borrowers, became the fifth US bank to fail this year as a housing bust and credit crunch strain financial institutions. The federal takeover of IndyMac capped a tumultuous day for US markets that saw stocks slide on a surging oil price and renewed fears about the stability of the top two home financing providers, Fannie Mae and Freddie Mac. IndyMac will reopen fully on Monday as IndyMac Federal Bank under Federal Deposit Insurance Corp supervision, but tensions ran high as customers at a branch at its Los Angeles-area headquarters read a notice in the window saying it was closed. At another branch down the road, a man who said he had more than $200,000 in an account - twice what is normally FDIC guaranteed - argued with a security guard who was closing up. The FDIC, which will seek a buyer for IndyMac, estimated the cost of the bank's failure to its $53 billion insurance fund at between $4 billion and $8 billion. “IndyMac is a company that was pretty much 100 percent invested in mortgage assets, and we're in a bad mortgage market, and it had no capital. It's not complicated,” said Adam Compton, co-head of global financial stock research at RCM in San Francisco, which manages about $150 billion. IndyMac joins top bank failures headed by the 1984 collapse of Continental Illinois National Bank & Trust Co. The Office of Thrift Supervision (OTS) insisted IndyMac's failure was the second-largest bank failure based on FDIC figures. But the FDIC said its data showed it was third behind the collapse of First RepublicBank Corp in 1988. The OTS, IndyMac's primary regulator, blamed comments by New York Democratic Sen. Charles Schumer for causing a run on deposits at the largest independent publicly traded US mortgage lender. Schumer responded quickly on Friday, blaming the OTS for not doing its job and allowing IndyMac's loose lending practices. “OTS should start doing its job to prevent future IndyMacs,” he said in a statement. Schumer questioned IndyMac's ability to survive the housing crisis in late June, and over the next 11 business days, depositors withdrew more than $1.3 billion, the OTS said. “This institution failed today due to a liquidity crisis,” OTS Director John Reich said. “Although this institution was already in distress, I am troubled by any interference in the regulatory process.” IndyMac was founded in 1985 by David Loeb and Angelo Mozilo, who also founded Countrywide, another big mortgage lender whose loans helped fuel the housing boom. Reuters __