“They say they want to save lives, but they risked killing people who were doing their job,” Mr. Salvini said. He also described the captain and the crew as “criminals,” and he railed against the government of the Netherlands for not intervening, since the Sea Watch flies a Dutch flag.

An Italian judge has 48 hours to decide whether to uphold Captain Rackete’s detention. Mr. Salvini said that she would be put on a plane to Berlin if she were released. “The Interior Ministry has an expulsion order ready,” he said, adding that the ship had been seized.

Captain Rackete’s Italian lawyer, Leonardo Marino, said by phone that his client had been detained on charges of violating an article of Italy’s Code of Navigation, specifically “resisting a war ship,” which carries a penalty of up to 10 years in prison on conviction. She is also under investigation for facilitating illegal immigration, he said.

Mr. Marino said his client was “very tired” because of the “intense pressure” she had been under. “She saved people at sea, and then asked for a safe port to bring them to, which was denied,” he said.

Riccardo Magi, an Italian lawmaker, boarded the Sea Watch on Thursday and was among the last to disembark on Saturday. He said in a phone interview that morale among the migrants on the ship had been low, and that he and other lawmakers had been trying to make sure they didn’t harm themselves.