SACRAMENTO, Calif. -- The National Transportation Safety Board announced Friday afternoon that catastrophic internal engine failure caused the crash of a Sacramento County Sheriff's Department helicopter.

The helicopter -- a Eurocopter EC 120 -- went down Wednesday night on a hillside near Lake Natoma.

NTSB officials said the helicopter engine's internal turbine blades disintegrated in flight.

"It broke. It simply broke," said NTSB investigator George Petterson.

Petterson also said that pockmarks found in the back of the helicopter were telling.

"That means that the engine is emitting some sharp metal objects. And as they hit the wall of the tailpipe, they're going to leave a pockmark," Petterson said.

The pockmarks coupled with soot scars left by the red hot metal hitting the tailipe was clear evidence of mechanical error, according to Petterson.

Undersheriff John McGuinness reacted to Friday's finding that no human error is suspected in the crash at this point.

"We do have some satisfaction knowing it was not pilot error," McGuinness said. "And for our mechanics who service the aircrafts on a regular basis, I think there's some relief on their part."

The sheriff's department has grounded its other EC 120 helicopters until more information about the crash is available.

"We don't want to run the risk of putting an aircraft back in the sky that perhaps is not worthy of that," McGuinness said.

NTSB officials are still investigating what caused the engine to disintegrate.

Officials said the helicopter's flight data recorder was recovered and is being sent to Europe, where the aircraft was made, for examination.

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Video: Early Investigation Results | Video: Department Mourns

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In the meantime, the department is mourning the two deputies killed in the crash.

The pilot, 36-year-old Joseph Kievernagel, of Citrus Heights, was married and a 17-year veteran of the department. The observer on the helicopter was 29-year-old Kevin Blount. He was a seven-year veteran of the department and was training to be a pilot.

Another deputy who was in the helicopter, Eric Henrikson, remains in critical condition at Mercy San Juan Medical Center.

Officials said the department's flight crews respond to hundreds of calls for service every week -- acting as law enforcement's eye in the sky.

Funeral services for the deputies who were killed will be held next week.