A suspected serial predator accused of sexually assaulting four women, killing two of them, was described by co-workers as a polite, soft-spoken car salesman who mostly kept to himself. Trent Christopher Benson made an initial court appearance Thursday and was ordered held without bond. The public defender's office was appointed to represent him, but a lawyer has not been named. Police in suburban Mesa said Benson has been charged with two counts of first-degree murder, two counts of violent sexual assault, three counts of kidnapping and one count of sexual assault.

Investigators watched Benson for a day before arresting him Wednesday and questioning him about four attacks that date back to 2004.

Police said Benson had a criminal record that includes arrests for soliciting prostitutes, which shocked his co-workers.

"This is unbelievable. It would be the last person that I would have expected," said Mike Fraccola, a used car dealer in Mesa. "He seemed happy in his everyday life."

However, Fraccola added that Benson "was always somewhat quiet and subdued. He was a little bit mysterious. No one really knows what he did with his spare time."

Bill Fralick, a former co-worker at the dealership, said Benson told him he enjoyed strip clubs.

But "there is no way, shape or form I would have thought him capable of harming anyone," Fralick said. "If I had kids, I would have let them be around him."

Authorities said DNA evidence links Benson to four female victims. The first was a 21-year-old who was found strangled and partially clothed in a west Mesa alley on Nov. 4, 2004.

Nearly three years later, on Oct. 14, 2007, a 44-year-old was found strangled and raped on a west Mesa street.

A Mesa woman was abducted and raped Aug. 16, 2007, but managed to escape. A 35-year-old Phoenix woman was abducted Nov. 4, 2007, behind a business and later was found unconscious by a passer-by.