An overcrowded funeral Tuesday for a U.S. federal agent killed in Mexico ended with three top Obama administration officials vowing for justice for his grieving family and another agent wounded in the bloody roadside ambush a week ago.

Immigration and Customs Enforcement Special Agent Jaime Zapata was fiercely dedicated to his job despite the risks, Homeland Security Secretary Janet Napolitano said.

"We will not stand for violence toward those who dedicate their lives for our protection," said Napolitano, while Zapata's family listened from a row of chairs near the open casket.

Later, during a graveside burial, the other agent shot during the Feb. 15 attack in Mexico placed a flower on Zapata's casket while seated in a wheelchair.

U.S. Attorney General Eric Holder and ICE Director John Morton also eulogized Zapata, and their appearance made for a prominent gathering of high-ranking U.S. officials in this part of the Texas border. Each paid tribute to Zapata and said the U.S. remaining undeterred in its effort to help Mexico end the violence by drug cartels, who are blamed for killing tens of thousands of people, including several Americans, in recent months.

"We will continue to stand shoulder to shoulder with our international partners and Mexican counterparts," Holder said.

He later added, "We must and will eradicate this scourge that took his life."

Morton mentioned Mexican federal investigators, military and customs as those who will rise to "honor and vindicate" Zapata.

More than 1,000 mourners packed a ballroom-sized hall at the Brownsville Events Center to overcapacity. Border Patrol and Customs and Border Protection agents, all in uniform, stood two-deep in lengthy lines along each wall. The room was filled almost entirely law enforcement personnel _ from Transportation and Security Administration workers to small-town police officers _ and even more people stood outside to watch the service on a video screen installed in the parking lot.

Among those inside was ICE agent Victor Avila, who was shot twice in the leg during the attack on Zapata's car in the San Luis Potosi state. He sat in a wheelchair near the Zapata family and Jaime Zapata's fiance.

Zapata, 32, and Avila were attacked when a group of Zeta drug cartel members in two vehicles forced Zapata's sport utility vehicle off a highway, U.S. Rep. Michael McCaul has said. Avila was released from a Houston hospital last week.

San Luis Potosi borders two northern Mexican states where the Zetas and the rival Gulf Cartel have waged bloody battles over territory. Zapata and Avila were temporarily detailed to the ICE attache office in Mexico City and were driving from the northern city of Monterrey to the Mexican capital when they were attacked.

Rafael Munoz, Zapata's cousin, said Zapata had not worked across the border often. Zapata was born and raised in Brownsville and hailed from a family with deep roots in law enforcement; Zapata has one brother who also works for ICE and another who works for Customs and Border Protection.

Jaime Zapata was stationed in ICE's Laredo office before his Mexico detail. He had previously worked for Border Patrol.

"Together, the United States and Mexico will bring the long, hard arm of the law down on Jaime and Victor's shooters," Morton said. "Together we will look after our people. Together we will continue to see that Jaime and Victor's work is done and that the rule of law triumphs over lawlessness and empty violence."

Bishop Daniel Flores was the first to speak, using imagery to describe the "evil" Zapata had been fighting.

"He knew that if the good do not fight for what is good the enemy is aggressive and will take our children," Flores said.

After the 1 1/2-hour funeral service, streets were lined on both sides by law enforcement personnel for nearly half a mile leading away from the venue, and firetrucks and flags marked the route to the cemetery where Zapata was to be buried later Tuesday.

Zapata is the most recent of a handful of Americans who U.S. officials say have been killed by cartel violence in Mexico.

A 59-year-old missionary riding in a pickup truck with her husband was gunned down last month, the husband told police. A similar chase last year on a U.S.-Mexico border lake ended with an American tourist being fatally shot while riding a Jet Ski, according to his widow.

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Associated Press Writer Schuyler Dixon in Dallas contributed to this report.