Still, prosecutors and regulators have spotted gulfs in the way financial institutions oversee suspicious cash transfers, according to the federal and state officials. Under the Bank Secrecy Act, financial institutions like banks and check-cashers must report any cash transaction of more than $10,000 and bring any dubious activity to the attention of regulators. The federal law also requires banks to have complex controls in place to detect any criminal activity.

The comptroller’s office, JPMorgan and Bank of America declined to comment.

The investigations are gaining momentum as concern is growing in Washington that illicit money is coursing through the American financial system.

Back in July the Senate Permanent Subcommittee on Investigations accused HSBC of exposing “the U.S. financial system to money-laundering and terrorist financing risks” between 2001 and 2010. The British bank, which is also under investigation by federal and state prosecutors, is suspected of funneling cash for Saudi Arabian banks with ties to terrorists, according to federal authorities with direct knowledge of the investigations. HSBC officials have pointed out that they had strengthened controls to prevent money-laundering and replaced employees tainted by the allegations. Standard Chartered maintains that “99.9 percent” of the transactions under scrutiny complied with that rule and involved legitimate Iranian banks and corporations.

The case against HSBC alarmed banking regulators, who wondered if monitoring flaws could be pervasive in the banking industry. The comptroller’s office, which lawmakers accused of missing warning signs about HSBC’s weaknesses, has stepped up its scrutiny of American banks in recent months.

In April, the regulator issued a cease-and-desist order against Citigroup for gaps in its oversight of cash transactions. The order cited “internal control weaknesses including the incomplete identification of high-risk customers in multiple areas of the bank.” A person close to the bank attributed part of the problem to an accident when a computer was unplugged from anti-money-laundering systems.

Citi did not admit or deny wrongdoing, but said in April that it had already undertaken many of the reforms required.

Federal officials are now examining whether problems run even deeper and if criminals have managed to exploit these vulnerabilities. An example of how criminals can evade the system surfaced publicly in a federal drug case in a Texas court this summer. Mexican drug cartels hid proceeds from cocaine-trafficking in two accounts at Bank of America, according to law enforcement testimony in the case, and some of the money was used to buy racehorses.