By Felicia Patinkin

Tomorrow is the 50 th anniversary of President John F. Kennedy's assassination, a moment when time stopped for so many Americans.

The Discovery Channel is marking the day with a new documentary, "JFK: The Lost Tapes," which includes never-before-heard audio from the police and Air Force One that capture the chaos of Nov. 22, 1963 when the telegenic president was cut down in the prime of his life.

The tapes add a new layer of context to that day that began with so much promise, starting with the routine and calm chatter on police radios before the president's arrival in Dallas. A police dispatcher and sergeant are heard discussing routine topics from the weather to the crowd estimate.

"Weather is good … I guess there's about 2,000 here," a police sergeant says on the tapes.

As Kennedy descended upon Dallas, with his eyes set on re-election in 1964, law enforcement had prepared for weeks for the visit, including the 10-mile motorcade.

"Whenever he was in a motorcade situation, where there were going to be crowds, he wanted the people to feel that he was close to them. And so the instructions were, top off," Former Secret Service Special Agent Clint Hill said in the documentary.

In police tapes broadcast for the first time, officers do their best to manage a larger-than-expected crowd.

"Drop back. We have to go at a real slow speed now," the Dallas police chief says, just before 12:30 p.m. when a pop is heard and the president is cut down next to his dazzling wife.

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"My job was to get up there and shield them," Hill recalled, the heartache still palpable in his voice 50 years later. "I jumped and ran… there was a second shot, they tell me, as I was running. I did not hear it."

It was pure panic. "I was yelling at the driver, 'Get us to the hospital. Get us to the hospital,'" Hill said.

The police tapes capture the frantic race to the hospital as the Dallas Chief of Police instructs: "Get these trucks out of the way! Clear everything."

Back at Dealey Plaza, a manhunt was underway for the shooter.

"I just talked to a guy up here who was standing here when the shots were fired at and he said he was standing real close to it and he believes they came from the Texas school book depository," a police patrolman says in the audio tapes.

At 1 p.m. CT, Kennedy is pronounced dead. He was 46 years old. For local cops, there is no time to grieve since one of their own, Officer J.D. Tippet, was just shot and killed. A suspect in his shooting is cornered at the Texas Theatre. His name: Lee Harvey Oswald.

Dallas Police Captain: You do have the suspect arrested in the Texas Theatre?

Dallas Police Sergeant: Yes sir, we have him and the gun.

Less than three hours after arriving in Dallas, President Kennedy boards Air Force One for a final time, and in the never-before-heard audio tapes, the White House and pilots discuss the delay before take-off at Dallas Love Field as Vice President Lyndon Johnson is sworn in as president.

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Air Force One: We're waiting for the swearing-in at the plane before takeoff.

White House: That's of volunteer? [Johnson]

Air Force One: Roger. We are waiting for judge to appear for swearing-in.

Mrs. Kennedy boarded the plane, still in her pink suit covered in blood.

"I looked into Mrs. Kennedy's eyes, and her eyes that had been so sparkling and bright before were absolutely dead, just… gone," Hill recalled.

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"JFK: The Lost Tapes" premieres tonight on the Discovery Channel.