MINNEAPOLIS (WCCO) — Investigators are struggling to find out why a Meeker County teenager shot his younger sister, the family dog and then turned the gun on himself.

The children’s father discovered the horrifying scene around 2:30 p.m. Monday when he returned home. Jessica and David Cunningham were at their rural farm house in Harvey Township. That’s about 13 miles northwest of the county seat of Litchfield in Meeker County.

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WCCO’s Bill Hudson spoke with the grieving father on Wednesday.

Everyone in the community is struggling to explain what would cause the 17-year-old boy, David Cunningham to do this. His father, Tom Cunningham, didn’t want to speak on camera. But he gave us some clues about his son’s growing despondence.

Tom Cunningham is trying desperately to cope with the horrifying scene. Returning from town, he saw the family’s German shepherd dead on the back step. Inside lay the bodies of his two teenage children.

“No, we have no motive at this point,” Meeker County Sheriff Brian Cruze said.

Cruze says investigators are still baffled as to why. What would cause 17-year-old David Cunningham to shoot his 15-year-old sister, Jessica, and the family dog, then turn the rifle on himself?

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“The investigation is ongoing. We hope to come across something, but we’ve had no luck as to why this happened,” Cruze said.

Jessica was being home schooled. David attended Atwater-Cosmos-Grove City High School.

“We don’t know, we don’t know why this happened,” Sherri Broderius said.

Broderius is both principal and superintendent at the school. Wednesday, counselors were helping students deal with their shock and grief.

“You know as a school we have to teach  kids about a lot of things, this is one thing we don’t want to teach about but that’s how it happens,” Broderius said. “It has a great impact on us. ACGC schools have a lot to deal with. There are a lot of kids who knew those who are involved, It’s going to cause a lot of heartache.”

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The father says he reassured his son everything would be OK despite his despondence and troubles in school.  Without being specific, both will be looked at as investigators struggle to come up with a clear motive for the killings.