MUSKOGEE, Oklahoma - Two people are in jail after a sexual assault investigation involving victims ranging from age four to 23.

Muskogee police said it's one of the most disturbing cases they've ever seen, and believe there could still be more victims.

Police said they have two of the victims in Muskogee, a 5 year old girl and 6 year old girl.

Investigators said a 23 year old recently came to them as well, and claimed she was sexually assaulted when she was four years old.

Police said some of the sexual assaults happened in a Muskogee home. The details of the assaults are uncomfortable for officer Lincoln Anderson to share.

"The things they were doing to these kids, and making these kids do, I don't know how anybody can understand it," he said.

Anderson said on March 25th, Muskogee police arrested 29-year-old William "Frankie" Dugan and 32-year-old Valerie Ojo on charges that include incest and sexual abuse of a child.

Investigators said the boyfriend and girlfriend sexually abused their daughters, ages five and six, on a regular basis since January.

They are concerned there could be more victims in Missouri and Ohio where investigators say Dugan lived before being arrested in Muskogee.

"Whether it be family members, or not family members, or ex-girlfriends' kids, there's no telling," Anderson said.

Police believe Dugan took pictures and video of the assaults on his phone and are working to get the pass code to unlock it.

If there are videos they want to know what he did with them and if he posted them on the Internet.

They also want anyone with information to call Crime Stoppers at 918-682-COPS.