A serial predator suspect charged with multiple murder and sexual assault counts was known to friends as a polite, soft-spoken car salesman in suburban Mesa who mostly kept to himself.

Trent Christopher Benson, 36, was arrested Wednesday and questioned about attacks on four women dating back to 2004.

Mesa police 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.

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.

Investigators had watched Benson for a day before arresting him and said DNA evidence connects him to the attacks.

Police said Benson had a prior criminal record that includes arrests for soliciting prostitutes.

That came as a shock to at least one of Benson's friends.

"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."

Authorities said Benson, who was raising his 7-year-old son alone, has a history of sex-related arrests.

He pleaded guilty in 2001 in Mesa Municipal Court to public sexual indecency and loitering, charges that prosecutors say are consistent in prostitution cases. He was sentenced to 10 days in jail, paid a $555 fine and was placed on probation for three years.

In May 1997, Phoenix police arrested and booked Benson into jail on suspicion of soliciting a prostitute.

Alisa Marie Beck, 21, was found strangled and partially clothed in a west Mesa alley on Nov. 4, 2004.

Authorities said Beck was the first of four victims linked to Benson by DNA evidence.

Karen Jane Campbell, 44, was found strangled and raped on a west Mesa street on Oct. 14, 2007.

The two other victims linked to Benson were sexually assaulted but survived the attacks.

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