SACRAMENTO — The National Park Service purposely destroyed evidence in the wrongful death case of a 9-year-old boy who was crushed by a retaining wall in a Northern California park, a federal magistrate judge said.

Magistrate Judge Gregory G. Hollows ruled Wednesday that Park Service officials intentionally demolished the retaining wall before investigators could examine it. As punishment, he recommended that the judge overseeing the case formally find the Park Service negligent in Tommy Botell's death. Such a finding by U.S. District Judge Garland Burrell would give a big boost to the Botell family's lawsuit.

Hollows' findings are not binding, and the final decision rests with Burrell.

Still, the magistrate was unstinting in his rebuke of the Park Service's handling of the case. He rejected the government's arguments that workers knocked down what remained of the wall shortly after the July 29, 2009, accident in Lassen Volcanic National Park because they felt it posed a danger to other hikers.

The magistrate said there was no need to destroy the wall because "there is no doubt that the scene of the accident, i.e., the remaining part of the wall, was important for investigative purposes."

He said Park Service officials could have closed the trail or erected a barrier around the accident site to preserve the evidence.

Instead, Hollows wrote, "it has become all too apparent that the defendant has purposely destroyed material evidence in this case."

He also found accusations that Park Service employees destroyed other evidence "highly suspicious," but said an evidentiary hearing would need to be conducted to determine for certain.

U.S. attorney spokeswoman Lauren Horwood said the litigation is still "in the early stages" and noted that the magistrate judge's findings aren't binding. The office has 13 days to file its objections with Burrell, Horwood said.

Lassen Park is in the southern Cascades east of Redding and is home to the southernmost volcano in that range.

Botell and his sister were hiking a trail ascending the 2,000-foot Lassen Peak and sat to take photographs atop a rock and mortar retaining wall. The wall crumbled, and a boulder weighing between 400 and 600 pounds crushed the boy.

His parents, Thomas and Jennifer Botell, and siblings witnessed the tragedy.

In 2011, Botell's parents, of Tehama County, filed a lawsuit in federal court alleging wrongful death, negligence and negligent infliction of emotional distress after the National Park Service denied their original claim. They are seeking damages.

Attorneys for the couple did not return phone calls seeking comment Thursday, nor did officials from the National Park Service.

Lassen Volcanic park spokeswoman Lisa Wilkolak declined comment, citing the pending litigation.

The government argues that Congress has protected it from wrongful death lawsuits like the one filed by the Botells, and is urging its dismissal.