SAN DIEGO (CBS 8) - Newly released recordings reveal that Dr. Thomas Bruff, the pilot killed in a small plane crash in the Los Angeles National Forest Sunday, lost contact with air traffic controllers moments before the crash.

The single-engine Cessna 182 was flying from Montgomery Field in San Diego to Santa Monica when it crashed into Brown Mountain. The last radar contact was around 8:30 a.m.

The audio recordings reveal the urgency in air traffic controllers' voices as they tried to communicate with Dr. Bruff because he was flying too low. Their efforts to get him to a higher elevation were met with silence.

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According to the audio recordings, Dr. Bruff was in constant contact with air traffic controllers as he made his way from Montgomery Field in San Diego to Santa Monica.

As he flew over Los Angeles, the 57-year-old pilot went silent.

Air traffic controllers repeatedly tried to reach him to warn him about his low altitude. All contact was lost with Dr. Bruff about six miles North of the Rose Bowl.

The white Cessna 182 aircraft with blue stripes was located about 4:30 p.m. Sunday at the 4,000-foot level about four miles north of the Jet Propulsion Laboratory. Six search-and-rescue teams worked for hours to locate the plane.

Dr. Bruff's body was recovered Monday night.

The FAA and NTSB are investigating what caused the crash.