An 18-year-old Camarillo teenager was stabbed to death by party crashers early Saturday morning at a high school graduation party in Moorpark, police said.

According to witnesses, Andrew John Singler was defending a friend who was had gotten into a fight with a group of uninvited guests when he was fatally stabbed at the home in the 4000 block of Hitch Boulevard in Home Acres, an unincorporated portion of the county just west of Moorpark.

At some point during the party a fight broke out between partygoers, and the victim was stabbed.

"There was nothing that anyone could have done to save him because the damage to his heart was irreparable," said Andrew's mother, Jacqueline Singler.

Several people were involved in the altercation, but no one realized a knife had been used until Singler collapsed, police said.

"It's a tragedy; kids need to be really careful for themselves," Jacqueline Singler said.

Andrew, who graduated high school last year, was on a first date with his new girl friend, his mother said. He went to the home to celebrate with a friend who graduated last week.

"I just want it to be known that Andrew was not a brawler who picked a fight," Jacqueline Singler said. "He was the one that kept the peace, and if his friends got into arguments he would try to mediate them."

Andrew is the youngest of three children. He leaves behind his parents, Charles and Jacqueline Singler, and siblings Katie, 26, and James, 24.

His mother said Andrew was a "real thinker" who enjoyed music and the arts. He also loved to cook with his sister, she said.

"Andrew was the victim of circumstances," Singler said. "It's a cruel world out there, and there is a lot of violence that we as parents didn't have when we grew up."

According to witnesses and sources within the sheriff's department, the suspects who killed Andrew may have been part of a Camarillo tagging crew.

Authorities were still investigating the homicide. No arrests have yet been made in connection with the crime as of Thursday.

"It is unknown at this time what prompted the fight," authorities said in a press release.

About 50 friends gathered for a candlelight vigil in honor of Andrew last weekend. A memorial service was held yesterday at Griffin Family Funeral Chapels in Camarillo.

The slaying at the Moorpark home was one of two in the county last weekend. Another young man died from stab wounds in Port Hueneme the night before.