KIEV, Ukraine — Volodymyr Danyluk was a Soviet Army veteran who joined demonstrations against Ukraine’s government last year. He was 55 years old, separated from his wife and mostly out of contact with his family, who saw him on live television during a winter of protests.

Then came the authorities’ crackdown last month in Kiev, the capital. The riot police and demonstrators clashed, scores of people were killed and the government of President Viktor F. Yanukovych fell. Mr. Danyluk disappeared from sight.

In the weeks since, Ukraine’s interim authorities have allowed opposition members to search prisons, morgues and hospitals for their missing. There has been no sign of Mr. Danyluk — or of more than 250 other missing Ukrainians.

After a season of political upheaval here, a gnawing worry persists: What happened to Ukrainians who seemingly vanished in their revolution’s fast-moving tides? Were Mr. Danyluk and the others victims of state repression and criminal activity by the police, or had some of them just drifted back to quiet lives?