The radical environmental group Earth Liberation Front -- known as ELF -- claimed responsibility, leaving a banner on the site saying, "If you build it, we will burn it."

Federal and local law enforcement officials have not arrested anyone in the case, despite a massive investigation and a $100,000 reward.

San Diego environmental and animal rights activists connected to the lecture that evening in Hillcrest confirmed yesterday that they have been called before the federal grand jury.

"The FBI are using this as an excuse to harass and intimidate activists who are trying to create a better world," said Michael Cardenas, an activist and independent journalist who said he testified Tuesday.

Agents at the FBI's San Diego office, which is leading the investigation, declined to answer questions about the case, as did federal prosecutors, citing the confidentiality of grand jury investigations.

The FBI also wouldn't reveal how many agents are investigating the University City blaze -- or fires the following month that burned four homes under construction in a housing development between Del Mar and Rancho Penasquitos.

ELF also claimed responsibility for those fires.

Last month, a top FBI official told Congress that "animal rights extremists and eco-terrorists" -- including ELF and a sister organization, the Animal Liberation Front -- pose "one of today's most serious domestic threats."

"Together with our partners, we are working to detect, disrupt and dismantle the animal rights and environmental extremist movements that are involved in criminal activity," John E. Lewis, deputy assistant director of the FBI's counter-terrorism division, told a Senate committee May 18.

He said such crimes are difficult to investigate because "extremists in these movements are very knowledgeable about the letter of the law and the limits of law enforcement."

He said the groups are loosely organized and their attacks require little equipment and funding.

The San Diego subpoenas coincide with an investigation in San Francisco in which animal rights activists were subpoenaed in the search for Daniel Andreas San Diego, a Northern California man wanted in the 2003 bombing of two companies in the Bay Area.

A lawyer for one of the people subpoenaed to appear in San Francisco yesterday and next month told the San Francisco Chronicle the investigation appears to be an excuse to intimidate protesters.

Local activists who have been subpoenaed said the FBI is turning on them because of a failed investigation into ELF.

"The questions aren't focused on investigating the fire," said David Agranoff, who sponsored the lecture about arson and other acts of environmental protest by activist Rodney Coronado, who served a 57-month prison term after being convicted of torching a Michigan animal-testing laboratory.

"The questions all seem to be very McCarthyist-like questions about the lecture," Agranoff said. "Who was there. What was said. ... What's wrong with a lecture?"

Agranoff said he has been subpoenaed to testify next Tuesday and has talked with others who have been questioned.

He said at least 10 people have been called before the grand jury here.

Activist Cardenas said he was subpoenaed to testify next Tuesday -- when supporters plan a rally -- but appeared two days ago because of a personal commitment.

He said he refused to answer most of the questions, invoking his Fifth Amendment right against self-incrimination.

He said he doesn't know who set the University City fire.

Coronado also denied knowing anything about the fire during a telephone interview from Tucson, where he is under indictment for allegedly disabling a mountain-lion trap.

Witnesses before the San Diego grand jury said most of the questions have to do with Coronado's talk.

"I was told that I definitely seem to be a target of the grand jury," said Coronado, who added he has not been subpoenaed or contacted by FBI agents.

He said he was in Tucson when the fire began at 3 a.m. August 1 and flew to San Diego later that morning.

Coronado, who is often quoted as a spokesman for the Earth Liberation Front, defended the arson.

"I totally support any action taken to preserve open space," he said. "It's the fault of developers themselves to not paying attention to the concerns of residents. ... It's become a legitimate response to urban sprawl."

Coronado spoke the evening of August 1, 2003, at The San Diego Lesbian, Gay, Bisexual, Transgender Community Center in Hillcrest.

Officials at The Center -- as it is commonly known -- said they rented out a room to Agranoff's group, Compassion for Farm Animals, and were not aware of the nature of the lecture.

FBI agents raided Agranoff's home a few weeks later and seized a video of the lecture; another activist said on a Web site that the FBI seized pictures he took that evening.

Agranoff said he's surprised by the focus on the lecture. It's unlikely, he said, that whoever set the fire would attend a talk by a convicted arsonist that night.

"It's obvious the FBI don't have a thing," he said. "They don't have a clue to what's going on. ... These are underground activists and they're wasting their time going after above-ground activists."

The fire didn't stop La Jolla Crossroads from being built. The complex's Web site says rentals will become available in the fall.

Copyright 2005, San Diego Union-Tribune.