OGDEN -- Three brothers have confessed to molesting their younger sisters, and a fourth has confessed to molesting his brothers.

The eldest brother said he molested his three younger brothers for six years, beginning when he was 10 years old. Prosecutors say his actions provoked the younger brothers to molest two of their younger sisters.The brothers pleaded guilty on Thursday in 2nd District Juvenile Court.

The oldest, who is now 18, pleaded guilty to three counts of sodomy on a child and one aggravated sexual assault of a child, all first-degree felonies. An additional sodomy count was dropped by the state in exchange for his confession.

"This is one of the saddest cases I've seen," said Weber County prosecutor Michaela Andruzzi. "It's like when you throw a pebble into the pond and watch the waves go out."

The three male victims in this case, now ages 17, 15 and 12, began molesting their two younger sisters beginning in 1993.

The 15-year-old boy pleaded guilty to fondling his then 5-year-old sister on a weekly basis beginning in 1996 and lasting until last month. He was charged with two counts of aggravated sexual assault of a child, a first-degree felony, and one count of sexual abuse of a child, a second-degree felony.

The 17-year-old boy pleaded guilty to one count of sex abuse of a child, a second-degree felony.

Charges against the 12-year-old brother were not made public because he is under the age of 14.

The parents of the boys made the initial report against their 17-year-old in January after learning he had fondled his 6-year-old sister in 1993. That investigation uncovered the allegations against the other brothers.

"We didn't even assume there were other children involved," said the boys' mother at the hearing. "We didn't know."

The oldest brother was sentenced on Thursday. He could be in a juvenile detention facility until the state is required to release him when he turns 21 years old. His sentence could have been longer had prosecutors decided to certify him as an adult.

All the brothers are being required to undergo psycho-sexual evaluations and attend therapy.

The 17-year-old was released from detention Thursday and placed under state supervised probation. Sentencing for the 15-year-old has been delayed until March 25.