Several days after announcing they believed to have discovered human remains which may have belonged to missing mom Susan Powell
, police searchers on Saturday abandoned the site after only uncovering charred wood.
"There's no resolution – and it's frustrating," Susan's dad, Charles Cox, tells PEOPLE.
Searchers dug up the wood after cadaver dogs alerted to human remains, although the dogs could also have detected an injury at the site and not a body, says Cox, who visited the search at Topaz Mountain in western Utah on Thursday.
He adds that it's possible, but not likely, that scientists examining the wood might learn more about anyone who came in contact with it.
The remote area is about 30 miles from where Susan's husband Josh Powell – the only person of interest in his wife’s disappearance – says he took his two young sons camping the night she disappeared from their Salt Lake City-area home.
Both police and the Cox family had hoped that the search would provide long-sought answers to the Dec. 6, 2009 disappearance, which police still classify a missing-persons case and not a homicide.
"We are very disappointed; we are frustrated," West Valley City Lt. Bill Merritt told the Salt Lake Tribune
. "We were hoping that this would be the answer everyone was looking for."