Three children have been found living alone in squalor with the decomposing remains of their nine-year-old brother.
Police discovered the youngsters aged seven, 10 and 15, after carrying out a welfare check at the flat in Houston, Texas.
Sheriff Ed Gonzales said the siblings were living in deplorable conditions and the body of the dead boy was on full display.
Police noted they had seemingly been abandoned by adults for a long period of time and were "fending for each other".
There were no signs they had been locked in the house and it is unclear if the children had called police for help.
Sheriff Gonzales said: "Very horrific situation here, very tragic.
"I've been in this business for a long time and I've never heard of a scenario like this, it really caught me by surprise.
"I think the oldest sibling was doing the best she could to take care of the others.
"Connecting all the dots, it seems they were in there while the body was deteriorating.
"We are trying to identify next of king to determine exactly what happened and how we got to this point... We're going to make sure we conduct a thorough follow-up investigation."
Houston County Sheriff's Office is investigating how long the children had been alone, as they believe it was likely more than weeks.
The circumstances surrounding the death of the youngster are also being investigated.
Homicide investigators along with child protections services are looking into the case.
Only one sibling may have injuries, but police said they were not going to disclose the extent of them at this time.
The surviving siblings have been taken into care and are being given counselling,
Neighbours said the management had been doing inspection rounds in the area for the last couple of weeks.
The mother of the children and her boyfriend have been found and are being interviewed by police.
