(CNN) -- A 35-year-old father found to be sane when he killed his three young daughters last July was sentenced to three life sentences without the possibility of parole Monday. St. Croix County Judge Howard Cameron said the lives of sisters Amara,11, Sophie, 8, and Cecilia, 5, were each so important that Aaron Schaffhausen had to serve each sentence consecutively. "Each child has to be recognized as an individual girl," Cameron said. "To make it concurrent would diminish what happened to those young girls." Schaffhausen and his wife Jessica had recently divorced when he came to spend the day with his daughters last year.
@highlight
Aaron Schaffhausen killed his three daughters, ages 5 to 11, last year
@highlight
Judge: The three life sentences must be stacked, not served concurrently
@highlight
Schaffhausen's attorney says his client suffers from mental illness
"Aaron Schaffhausen, the man who helped genetically make those girls and shape them ... @placeholder became the darkness, the boogeyman, and the monster under the bed," Stotz said.