Tylar Marie Witt, the 15-year-old accused of killing her mother, will stand trial as an adult, El Dorado County Superior Court Judge James Wagoner decided Tuesday.

"This was not an easy decision to reach," the judge said.

Wagoner said Witt's alleged involvement in the crime "shows criminal sophistication on the part of Miss Witt."

He said the evidence is unclear whether the girl actually spiked her mother's drink with drugs on the night of the killing, but it pointed to the fact that she called her boyfriend and let him into the house before Joanne Witt, 47, was killed.

"The court can think of no greater crime than matricide ... to participate in the death of the very person who gave you life," Wagoner said in his ruling.