Ivan Cepeda Castro remembers the day in every harrowing detail. It was Aug. 9, 1994. His father, a Colombian senator, poet and journalist, was being driven through the streets of Bogota. Suddenly shots rang out, and a car sped away in traffic. Cepeda Castro, passing the scene en route to a separate meeting, found his father slumped over in the front passenger seat, blood streaming down his face.

"I knew it had been a fatal shot," he said in an interview here this week, grimacing at the memory.

The assassination of Sen. Manuel Cepeda Vargas, a leader of the leftist Patriotic Union party, by right-wing paramilitary gunmen silenced a man who had championed labor unions and peasant movements, written poems of social protest and given a voice to marginalized groups in Colombian society.

At the same time, it galvanized his son, now 43, to begin a crusade of his own: to keep alive the memories of victims of political violence in his country -- including more than 3,000 members of the Patriotic Union -- and to seek justice for thousands of men and women who died or disappeared without a trace, removed by hidden hands of power and evil.

Cepeda Castro is in Washington this week to speak to administration officials and members of Congress from the victims' point of view, at a time when Colombia's government, with U.S. support, is launching a program that offers legal amnesty and job training to former paramilitary members who hand over their arms.

"We are not looking for vengeance," he said. "We have not chosen to respond in the same way as our oppressors, but we all have a civil and political responsibility. Victims and survivors have the moral authority to talk about their issues, but not to lose sight of the whole picture." Of the amnesty program, he added, "We don't want U.S. dollars to be given to anyone who does not have to give up anything significant for peace."

Cepeda Castro grew up in an environment of political turmoil. As a young boy in 1965, he was taken to Czechoslovakia after his father was jailed for a year and sent into exile for five more. There he witnessed Soviet tanks rolling into Prague in 1968.

"Father liked to define himself as a man who lived by his principles," said Cepeda Castro. "He said we needed to act in situations of injustice and to never lose sight of segments of society who had been left out or excluded."

After returning to Bogota in 1970, Cepeda Vargas resumed his political and journalistic crusading. He was often accused of being a rebel ideologue. There were anonymous threats and police raids. Friends and colleagues were killed.

Although his parents were well-educated, Cepeda Castro recalled, they went without personal luxuries. His mother, who never wore jewelry or makeup, became a member of the Bogota city council shortly before dying of a brain tumor in 1978.

In the mid-1980s, a negotiated accord between leftist guerrillas and the government enabled the Patriotic Union to be represented in the legislature, and Cepeda Vargas was elected to the Senate. The experiment succeeded briefly, but later the guerrilla groups forged alliances with drug traffickers, while paramilitary groups set out to eliminate the political left.

At the time Cepeda Vargas was killed, his son said, he had been working to establish negotiations between guerrillas and a new government. At the time, the assassination made big headlines, but soon killings of activists on the left became commonplace, he said.

From 1966 to 1998, some groups report, there were 42,000 abductions and extrajudicial executions in Colombia. Another report said more than 14,000 people had been killed by state agents and paramilitary groups.

The victims' relatives, Cepeda Castro said, were often stigmatized for life, viewed as guerrilla sympathizers and ostracized from society. They were denied bank loans and their children were denied admission to certain schools.

"Regardless of what you think of the Communist Party or the Patriotic Union, this is unacceptable," he said. "Our work is to open up a space for public debate. Guerrillas are widely known as authors of humanitarian crimes, but it has never been clearly accepted that some state sectors have been involved."

Cepeda Castro said he believes that reconciliation in Colombia must involve the victims and civil society, not just groups that took up arms. If a national reconciliation commission is formed, he said, it cannot also act as a truth commission. "The government cannot be both a judge and a party in the process."

Despite his pacific demeanor and message, Cepeda Castro said he was in danger at all times. Peace Brigades International, a human rights organization, has provided him with physical protection. "We don't go out at night and do not take unnecessary trips. We are always on the lookout for anything unusual," he said.

Still, he said, "I feel happy because my life has meaning." Many victims and survivors have had to live in silence, he explained. "I can exert certain influence in certain spaces and I can express what I feel."