West Mercia Police have recovered a knife and one line of inquiry detectives are following is that Mr Fuller killed the children before taking his own life.
The force launched a murder investigation but described the deaths as a "tragic family situation" and are not looking for anyone else.
I can disclose that a weapon has been recovered from the scene. Officers involved in the search found a knife in the vicinity of where the bodies were found. It will now be forensically examined. One line of inquiry being considered is that the father took the children's lives before taking his own."
The grandfather of the four members of a Gloucestershire family found dead in a disused Shropshire quarry has written a heartfelt letter.
Test results are due back today confirming how three children and their father died at a beauty spot in Shropshire.
Tributes have been paid to three children found dead at a beauty spot in Shropshire.