HEIDELBERG, Germany — Testimony continued Tuesday in a case against an American woman and her Turkish fiancé accused of plotting to bomb a U.S. base.

Several German investigators and an FBI agent testified. The court is waiting to hear key evidence from an American woman who tipped off police last summer.

German authorities have accused Astrid Eyzaguirre, 23, of assisting Osman Petmezci, 25, in a plan to use homemade bombs against a U.S. installation in Heidelberg. In court last week, the couple denied planning such an attack.

German police arrested the couple Sept. 5 after investigators found gunpowder, pipes and chemicals that could be used to make explosives in their home in nearby Walldorf. Eyzaguirre worked on base at an Army and Air Force Exchange Service liquor store.

Dozens of spectators and reporters gathered in the gymnasium-size courtroom Tuesday to hear the evidence presented. FBI agent Jason Day testified to his dealings with an American woman named Christi Allen, said German prosecutor Joerg Richter.

Allen knew Eyzaguirre and alerted officials of the alleged plan last summer, he said. When Allen left Germany for the United States, it created an inconvenience for both the prosecution and the defense.

“Her testimony is very important,” Richter said. “We all want to have her here.”

Germany has no legal right to force Allen to speak before the court. However, she will give testimony via video-teleconference on April 25 if she decides not to return to Germany, Richter said.

“We’re waiting,” Richter said. “She still has not said if she will come.”

Also on Tuesday, witnesses who knew Allen testified that she was not a reliable source, Richter said.

Court continues Wednesday, then breaks for the German Easter holiday and resumes on Tuesday.