Finding the bodies of an entire family puzzles the American police.. What is the story?

US police opened an investigation on Wednesday to reveal the timing and cause of the death of 5 members of a family in Utah, including 3 children.
The bodies were found in the home of the dead after a relative became concerned because there had been no news of them for several days.
The body of a wounded 17-year-old, who appeared to have been shot, was found in the garage of the home on Tuesday.
As of Tuesday evening, police in the West Valley suburb of Salt Lake City did not know whether this young man was a suspect or a victim in the case.

Communicate with the injured person

Police spokeswoman Rosanne Fainoco said that due to the injuries this young man suffered, “there are some difficulties in communicating with him and finding out more information.”

She explained in a press conference on Tuesday that authorities do not believe there is a suspect on the loose, and that the crime “was limited to this house only.”
The police announced that they expect to provide more information in the coming hours.