Police say the suspects, Debby Frank and her daughter Rosa Frank, would accompany the victim to the bank and stand next to him at the teller to negotiate his withdrawals.
The women allegedly took $20,000 in cash, $2,700 for a new computer from Best Buy and another $30,000 for a Mercedes-Benz M350.
"He's a very trusting man," said Lt. Ray Garcia of the El Segundo Police Department. "He's 90 years old, his memory is not all there."
Debby Frank was arrested at her tarot card readings and psychic business in Harbor City last week. She was charged with felony elder abuse.
Rosa Frank remains at large.
Detectives say the women's operation began to unravel when police received a call from a Bank of America branch about an elderly man trying to take out $10,000 from his account and was confused about why.
"I would describe them as true predators," Garcia said. "The teller became a little suspicious when he didn't know why he was withdrawing it, other than that he was going to give it to some people that he couldn't name."
According to Garcia, the women were in the process of having the victim buy them two high-end cars totaling $150,000.
The women have allegedly been involved in similar crimes in San Diego County and other areas of the South Bay.
Anyone with information is asked to call El Segundo detectives at (310) 524-2216.