Federal authorities seized roughly $20 million in cash hidden inside a mattress in a Westborough apartment this week and arrested a Brazilian national in connection with the sprawling TelexFree fraud case, US Attorney Carmen M. Ortiz’s office said Thursday.

In a statement, prosecutors announced the seizure and arrest of Cleber Rene Rizerio Rocha, 28, on a charge of conspiring to commit money laundering. Rocha was ordered held during his initial appearance Thursday in federal court in Boston. He did not enter a plea.

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