TULSA COUNTY, Oklahoma - Just in the past month, three children have been murdered in our area. Detectives said all three are victims of child abuse - two are also victims of sexual abuse.

There have been nine child deaths in Tulsa County this year alone, and, at least, two in Washington County. Not all are connected to child abuse, but investigators said the few that were are some of the most heinous cases they've seen in quite some time.

Pictures show their innocence; 4-year-old Jaydenn Hansche playing in a cardboard box and 16-month-old Sawyer Jefferson fascinated by ducks, or in the arms of her mother. Investigators said both little girls were murdered after enduring unimaginable sexual abuse.

Then, there's Neveah Roldan; detectives said she was shaken to death and died on her first birthday.

“I'm not going to pre-judge anything about it, it's alarming,” Tulsa County District Attorney Steve Kunzweiler said. “You just don't see those kinds of horrific injuries, and I don't know that I'll ever have an explanation for why.”

In each case, the mother's boyfriend is accused of murder.

Michael Nordbye is charged with raping and murdering Jaydenn; Cody Johnson is in jail, accused of raping and killing Sawyer; and Nathaniel Watkins is charged with the murder of Neveah.

None of them were the biological father; all of them, detectives said, were alone with the child at the time of the abuse.

“Often times, in those cases, he is unemployed, and mom is working. Money's tight...so, instead of paying lots of money for daycare, they figure, 'he's sitting at home all day, he can watch the child,'” said child crisis detective, Corporal Greg Smith.

He said, in the shaken baby case, there were signs of abuse in the past the mother ignored, which is why investigators said Halleluiah Brookens was arrested.

Smith said, “Those, we felt, should have been a warning to her and she should have taken some steps to protect the child and prevent future injury, and when she didn't the child suffered a fatal injury.”

According to Washington County court records, Jaydenn's mother, Courtney Hansche, bathed and washed her unconscious child’s clothes before taking her to the hospital. She is charged with murder, rape, child abuse and neglect.

But, with young Sawyer, Smith said there was no suspicious history with the mother's boyfriend; the two had been together for about seven months.

“The injuries inflicted by the sexual abuse maybe could have been fatal by themselves. The physical abuse that was inflicted in relation to it could be have been fatal all by itself. That was a very heinous case,” Smith said.

Kunzweiler said the allegations are all disturbing and hard for those working on the cases, but its work they’re doing with a purpose.

“The load is going to be heavy for us for a long time just because of what's happened in this last year. I have no way to explain it, I've seen a disturbing pattern or trend that's developing, and we need to get a handle on it,” Kunzweiler said. “I still have to ask people in my office to do something to bring justice to the children whose lives have been taken too early.”

Investigators and the district attorney said letting unstable boyfriends babysit can be a risk. They said if single mothers can, she should have a family care for the child.

Detectives said many abuse cases are almost impossible to predict, but one sign could be when a single mother withdraws from family and friends after getting a new boyfriend.

“When you make a decision to bring a child into this world it is your responsibility from that point on to make sure that every bit of that child's life is protected,” Kunzweiler said.

He said the DA’s office is going to be reaching out to professionals in the community to help identify areas where they can get a proactive message out to parents.