PALMER -- The Palmer District Attorney's office has accused Zebulon Whisler, a 24-year-old cook in a Wasilla bowling alley diner, of serial rape, charging him with 15 counts of felony sexual assault against six women.

Whisler was indicted on five counts of sexual assault last month, charged in that case with forcing himself on a date while they were parked and stargazing on Lazy Mountain.

In court Thursday he added 10 more not-guilty pleas to the five already on record.

According to information filed in court, the new claims stem from incidents that happened between 2003 and 2009. They were uncovered during the investigation of the first case, officials said.

Alaska State Trooper spokeswoman Beth Ipsen said the women apparently all knew Whisler before the attacks happened.

"He met them through a variety of ways -- some through the Internet, some through friends," she said.

Ipsen would not provide more details because it could compromise the ongoing investigation, she said. And it might reveal too much information, allowing people to identify the victims.

Trooper investigator Ramin Dunford said the five women did not come forward on their own but were found while troopers investigated a Jan. 23 sexual assault report. According to the indictment, the five additional women said Whisler either touched them inappropriately or had sex with them without their consent.

Ipsen said victims often don't report being raped.

"People tend to be ashamed and embarrassed because sexual assaults can take away a lot of self-esteem from a victim," Ipsen said.

According to police reports, the first victim said Whisler picked her up for a date on Jan. 22 in a red Ford Ranger. He drove to a Palmer bar and they later went stargazing on Lazy Mountain east of Palmer. According to her report, it was while the couple was parked that the assault happened.

The woman told troopers she "was scared because Zebulon was so big." Whisler, according to a trooper affidavit, is 6-feet, 8-inches tall and weighs 240 pounds.

The charges from that incident range from forcibly touching the woman's breasts and genitals to forcing her to have both vaginal and oral sex.

Whisler is being held on $50,000 cash-only bail. Palmer Superior Court Judge Vanessa White on Thursday refused to allow Whisler to go home with any of the five people who offered to be his required third-party custodian, meaning they agreed to watch over him 24 hours a day, make sure he obeyed bail conditions and showed up for court hearings.

His parents, Dean and Tina Whisler, were rejected after state prosecutor Kerry Corliss told the judge they had interfered with the troopers' investigation. Corliss said the Whislers believed the charges "were false or trumped up," and that one parent "tried to drive away in the vehicle that the state said was evidence." Dean Whisler is a correctional officer at Palmer Correctional Center near Sutton.

Tiny Virginia Courson, a longtime family friend, was rejected because she had no prior experience as a third-party custodian, had four teenage sons and planned to be gone from the state soon. Layne Henson, a friend of Whisler's who goes to church with him, was rejected because he had recently gotten a job that limited the amount of time he was free to watch Whisler. Another family friend who stepped forward, Sonjah Schumacher, was rejected because she also had a busy schedule. The 68-year-old retiree told the court she cares for her paraplegic son.

Judge White said none of the family friends who applied were strong enough candidates for the job but she left the door open for a stronger candidate if one emerged.

Whisler's attorney argued that his client has no criminal record. The prosecution said he has a record in Oregon but did not go into detail.

If (the charges are) true, Mr. Whisler is a serial offender and presents a palpable risk to the community," White said.

Ipsen said after the hearing that troopers believe Whisler may have assaulted other women. She encouraged other victims to call Mat-Su Crime Stoppers at 745-3333.