Magistrate Judge Arlander Keys said the defendants clearly knew the charitable funds they sent to Palestinian groups on the West Bank were destined for Hamas and that the group was involved in terrorism.
Stephen J. Landes, an attorney for the parents of the slain David Boim, said it was the first time a court had held U.S.-based organizations liable for terrorism abroad.
Keys ordered a Dec. 1 jury trial to decide how much must be paid by Texas-based Holy Land Foundation for Relief and Development, the Islamic Association for Palestine and alleged Hamas fund-raiser Mohammed Salah of Chicago.
"This is a huge win for victims of terrorism," Landes said. "It shows the law works."
Boim's parents are seeking $600 million, though attorneys say there's little chance of collecting that amount.
Boim, 17, a yeshiva student, was shot and killed in 1996 while waiting for a bus in the West Bank. One of his Hamas attackers was caught and sentenced to 10 years in prison; the other died in a 1997 suicide bombing.
Boim's parents claim money from the charities found its way into Hamas coffers and therefore financed the type of violence that killed their son.
Holy Land Foundation attorney John Boyd said the charity had been unfairly singled out and called it "an enormous disappointment" that the judge found it liable before the case could go to a jury.
Attorney Brendan Shiller, representing the Islamic Association for Palestine, said the judge's decision "dangerously stretches theories of liabilities so you no longer have to prove cause and effect."
"We're definitely going to appeal," he said.
The defendants deny any ties to Hamas and argue that there was no evidence to show that money they sent to charities on the West Bank was tied to the Boim killing.
Keys, however, said the Boims didn't need to show that.
"Rather, the Boims need only show that the defendants were involved in an agreement to accomplish an unlawful act and that the attack that killed David Boim was a reasonably foreseeable consequence of the conspiracy," Keys said.
Keys made his decision without a trial — a "summary judgment" — that Salah and the two groups were liable based on evidence presented in court papers. He said the evidence was clear.
If the trial goes forward as planned, the jury will be asked to decide if a fourth defendant, Quranic Literacy Institute, must pay damages.
Boim's parents say the institute also is to blame because Salah worked there while allegedly raising funds for Hamas.
Quranic Literacy attorney John Beal said his clients "have maintained all along that they have absolutely nothing to do with the funding of Hamas."
Salah's assets have been impounded by the government, which wants them forfeited. He was indicted in Chicago in August with two other men on charges of financing terrorism and faces years in prison if convicted.
Holy Land Foundation's funds were impounded following the Sept. 11, 2001, attacks, and the group was charged in Dallas in August with funding terrorism.