But a senior German official said Friday that there might not be enough evidence to prosecute the second official for spying for either Russia or the United States.

The two sides are now beginning to turn to the task of repairing the German-American relationship.

The German foreign minister, Frank-Walter Steinmeier, will meet Secretary of State John Kerry on Sunday on the sidelines of one of several important American-German joint efforts: negotiations over limiting Iran’s nuclear ability. As Mr. Steinmeier said Friday, the expulsion of the American intelligence official was an inevitable step once it became clear that the United States, long revered for championing democracy after the end of Nazi rule, was spying on Germany. “We need and expect a partnership based on trust,” he said.

For now, a senior German official said, the spying “overshadows everything we do.” In order not to appear to be kowtowing to the Americans, Ms. Merkel needs “something” from Washington, this official said.

Germany clearly depends on the United States for its security and, the official estimated, shares 80 percent to 90 percent of its intelligence with Washington. As Ms. Merkel noted in Saturday’s television interview, “We work very closely with the Americans, and I hope that will continue.” So what the United States might give her is not yet clear. Equally murky are the many unanswered questions. Did Markus R. really meet his handlers, as reported, in Austria? Was he even, as Der Spiegel reported on Saturday, run from the American Embassy in Vienna? If so, will ruffled Austrians limit American intelligence operations in their country? How did Markus R. get away with making hard copies of the 218 documents — which filled five large binders — taking them home, scanning them, sending them to his American handlers and storing them on a USB stick found by investigators?

Guards at the federal intelligence headquarters at Pullach, outside Munich, have no right to conduct body searches of roughly 5,000 employees, said Clemens Binninger, a parliamentary deputy of Ms. Merkel’s center-right party who heads the commission on the secret services. And “you can’t possibly search everyone,” he said.

For Mr. Hahn, who sits in Parliament for the Left Party of former East German Communists and Western leftists, the story proves that, like any good spy, you should never rule out anything.

“In both cases, we only started probing because people believed it involved the Russian secret service,” Mr. Hahn said. “For me, the discussions of the past few days have shown that we think the Russians and Chinese are willing to do anything. But in the Americans we placed literally blind trust, and this trust is now really shaken.”