In September 2015, he traveled to Beijing to try to file a lawsuit against Yushu officials for not properly supporting the Tibetan language, but failed to do so. He was quoted later that year in two Times articles on Tibetan language and culture written from Yushu, and he was the centerpiece of a nine-minute Times documentary video. He had come into contact with Times journalists in May while on an exploratory visit to Beijing and insisted on doing on-the-record interviews.

Mr. Liang, the lawyer, said the police case files, which he had seen on a June visit to Yushu, showed that the police had focused their investigation on Mr. Tashi’s interviews with The Times, which were conducted by this reporter and Jonah M. Kessel, a video journalist. He said the police were especially incensed by the video, produced by Mr. Kessel. (One section of the police case files mistakenly names additional people as producers.)

Mr. Liang, who was retained by Mr. Tashi’s family, met separately with Mr. Tashi and the Yushu police chief.

“I met with Tashi in the detention center for more than one hour,” he said. “Tashi was doing well. He thinks that what he did wasn’t wrong. Tashi said he had had no intention of inciting separatism.”

In his interviews with The Times, Mr. Tashi never advocated Tibetan independence. He said Tibet should remain under Chinese governance and called instead for greater regional autonomy, especially in language use and education. Mr. Tashi also praised Xi Jinping, the Chinese president and Communist Party chief.

“All he wants is to try to preserve Tibetan culture,” Mr. Liang said.

He added that it was possible that prosecutors could ask the police for further investigation into Mr. Tashi and delay the decision on whether to bring the case to court.