Emergency workers gather outside the damaged Oklahoma City federal building after the 1995 attack

OKLAHOMA CITY (CNN) -- After an 18-month probe, the grand jury set up to investigate rumors of a wider conspiracy in the 1995 Oklahoma City bombing found the two men now in prison for it acted alone.

But the latest conclusions have failed to satisfy some of those who have insisted more is still unknown about the events that left 168 dead and 500 injured.

The grand jury, which disbanded Wednesday after delivering a 21-page report, brought a single indictment; it remained sealed Wednesday night pending an arrest, said First Assistant District Attorney Patrick Morgan, who oversaw the 14-member citizen panel.

"We cannot affirmatively state that absolutely no one else was involved in the bombing of the Alfred P. Murrah Federal Building," grand jurors reported. "However, we have not been presented with or uncovered information sufficient to indict any additional conspirators."

Timothy McVeigh was convicted of setting off the April 19, 1995, bombing, and his ex-Army buddy, Terry Nichols, was convicted of assisting McVeigh. McVeigh, 30, was sentenced to death; Nichols, 43, to life imprisonment for helping to plan the attack. A third man, Michael Fortier, 29, is serving a 12-year sentence for not warning authorities about the plot.

The grand jury said it found no credible evidence that the bombing was linked to white supremacists or foreign terrorists, concluding that it was an act "perpetrated by Americans on Americans." And they dismissed theories that federal agencies knew about the bombing and failed to prevent it.( 249 K/5 sec. AIFF or WAV sound)

Burkett says the grand jury's purpose was to separate fact from speculation
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"We can state with assurance that we do not believe that the federal government had prior knowledge that this horrible terrorist attack was going to happen," the grand jury's report stated.

And grand jurors said "the most likely identity" of the elusive John Doe #2 -- a mystery man supposedly seen with McVeigh in the days before the bombing -- was Todd Bunting, another customer in the Junction City, Kansas, Ryder truck rental facility where McVeigh got the vehicle used in the bombing.

Federal investigators cleared Bunting of any involvement and said he was a victim of mistaken identity.

Some remain unsatisfied

The grand jury was impaneled after a petition drive led by former state Rep. Charles Key and Glenn Wilburn, whose two young grandsons died in the bombing.

Grand jurors heard 117 witnesses, but Key said Wednesday he still doesn't think the truth has been told.

Nichols

"There's clear and convincing evidence that there were others involved," he said.

"They should bring everyone to justice, and that is what we want," Key said. He said his Oklahoma Bomb Investigation Committee would release its own report within 60 days.

And Stephen Jones, the lawyer who represented McVeigh, called the grand jury report "a whitewash" that repeated the government's prosecution theory.

"Clearly there was a John Doe #2," he said, and to suggest otherwise is "an insult to the evidence."

"I think that the last opportunity to find out the rest of the story ended today," Jones added.

McVeigh

The grand jury was set up over the objections of Oklahoma Attorney General Drew Edmondson, who called it "the worst kind of paranoid conspiracy pandering."

"I'm proud of them for their diligence and thoroughness and not surprised with the outcome," Edmondson said Wednesday.

District Judge William R. Burkett, who oversaw the grand jury, said that its report will satisfy many of those who had serious questions. But he worried that "others will simply now include these jurors as the newest members of the conspiracy."

The grand jury called on Bob Macy, the district attorney in Oklahoma City, to carry through with his plans to bring state murder charges against McVeigh and Nichols once their appeals of their federal convictions are exhausted.

The Associated Press contributed to this report.