The four were killed by a 26-year-old parolee, who also died in the gunfight Saturday, authorities say.
The officers' caskets were draped in American flags and shepherded to the arena in caravans that passed under a giant U.S. flag held up by two fire truck ladders as they entered the parking lot.
Pallbearers accompanied the caskets inside the venue while bagpipes sounded throughout the space at the beginning of a solemn ceremony packed with law officers from far and near.
New York City Police Lt. Tommy Ng, attending the ceremony, said last week's tragedy brought back some memories of Sept. 11. He said he is not surprised from the outpouring of support his colleagues in Oakland have received.
"When one of us is hurt, all of us are hurt," Ng said before the service. "We're all brothers."
Before she headed inside, Norma Jean Palmer, 55, of nearby Alameda, hugged longtime Oakland police officer John Wilson as he greeted fellow officers from across the country.
"You keep your head up," Palmer told Wilson, who nodded slowly.
Wilson, 49, who grew up in East Oakland, said this has been the toughest week in his 25-year career.
"It's been hard, but we're getting through it," Wilson said. "The support we have from our colleagues near and far is much appreciated."
Wilson said he knew all four of the officers killed and promised that their memories will live on.
"They made the ultimate sacrifice," Wilson said. "They will never be forgotten."
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