IN THE final years of his life, Boris Nemtsov never gave up on politics in Russia, even when many others were discouraged or frightened away from standing up to President Vladimir Putin. Mr. Nemtsov, once in the front ranks of Russia’s post-Soviet reformers, in the last decade and a half became a persistent Putin critic. To some, he was a cheerful yet faded political figure. But he was stubborn, sustained by the hope that if only he could get the word out, if only he remained engaged, Russia could recover a chance for democracy. He published reports calling attention to Putin excesses, such as the lavish preparations for the 2014 Sochi Olympics, which he said “highlighted the main flaws of Putin’s system in a nutshell: Lawlessness, corruption, high-handedness, cronyism, incompetence, and irresponsibility.”

Last year, Mr. Nemtsov was consumed with the war in Ukraine, triggered largely from the shadows by Mr. Putin. While igniting battles that left thousands dead, the Kremlin leader insisted Russian troops were not in Ukraine, armed unrest was of local origin and Russia was not directing the insurrection. Mr. Putin waged what has been called a “hybrid” war of deception, subversion and violence.

This was fertile territory for Mr. Nemtsov. He frequently received death threats but was not intimidated. On Jan. 27, he sent the Russian prosecutor general a formal request asking him to verify information about Russian soldiers killed in Ukraine. Mr. Nemtsov had some insight into the true situation; family members of soldiers were telling him about coffins coming home to Russia. Mr. Nemtsov’s idea was to write a report, “Putin.War,” and, as he told his colleagues, “publish it in huge numbers and hand it out on the streets. We will tell how Putin unleashed this war. That is the only way to defeat propaganda.”

On Feb. 27, Mr. Nemtsov was fatally shot in the back while walking on a bridge within sight of the Kremlin walls. The gunmen were arrested, but whoever ordered the murder has not been charged. This week, Mr. Nemtsov’s allies and friends in Moscow published the report that he was working on at the time of his death about the war in Ukraine.

Like Mr. Nemtsov’s other projects, the report captures ground truth that is rarely, if ever, documented these days in Russia. Mr. Nemtsov’s reports were never perfect, but his stubborn refusal to give up was inspiring. In this case, he and his colleagues found that at least 220 Russian soldiers have been killed in Ukraine; that Russian authorities marshaled mercenaries by taking part in the recruitment, arming and financing; that the war has cost Russia more than $1 billion; and that it has been directed from the Kremlin by Vladislav Surkov, one of Mr. Putin’s top aides.

Mr. Nemtsov’s last act for his country befits his long pursuit of a Russia open and free — at a time when it is neither.