Gary Cain, who worked as a company consultant for a now-defunct oil field fracking sand company, testified in his own defense Wednesday.
Cain, along with state Sen. Carlos Uresti, is on trial facing federal fraud and money laundering charges.
The government alleges that the pair were part of a Ponzi scheme that convinced investors to buy into FourWinds Logistics.
The investors were told that FourWinds was buying fracking sand and selling it to oil field companies.
"I knew nothing about the sand ... who was buying it or where they were buying it from," Cain testified.
Cain said that when he learned that FourWinds CEO Stan Bates was using corporation funds to buy high-dollar cars and prostitutes, Cain told Bates "it was illegal" and he "would help him find a lawyer."
Bates pleaded guilty last month to eight felony charges and is awaiting sentencing.
Cain testified that he never had access to false spreadsheets that showed the company was making money.
Cain and Uresti are facing a combined total of 20 charges.
Closing arguments in the trial could come as early as Friday.