Image Mr. Yanukovych before signing a pact that he thought would keep him in power. Credit... Sergei Supinsky/Agence France-Presse — Getty Images

Around 2 p.m. that Friday, just as European diplomats were gathering for the signing ceremony at the nearby presidential administration building, Mr. Tereschenko received a call from a deputy interior minister, Viktor Dubovik, with an order to leave the city. Mr. Dubovik, he said, put him in touch with the opposition lawmaker Mr. Pashinsky, who escorted the Berkut commander and his 60 or so men to the edge of town, from where they drove overnight by bus to Donetsk.

Mr. Dubovik, who the authorities say has since fled Ukraine, could not be located for comment.

Mr. Pashinsky estimated that in all, he arranged escorts out of the city for more than 5,000 officers from the riot police, Interior Ministry forces and other security units, like the special operations unit, Alfa. He said Mr. Dubovik was just one of the officials he worked with on the mass evacuation, but added that he did not know where the order to retreat had originated.

Giving Up on a Leader

Inna Bogoslovskaya, a longtime ally of Mr. Yanukovych who broke with him over his November decision not to sign the trade deal with the European Union, said the retreat was merely a response to a resolution adopted late Thursday that week by the Ukrainian Parliament that ordered all Interior Ministry troops and police officers to return to their barracks.

Ms. Bogoslovskaya said that the Thursday night vote sent an emphatic message to Mr. Yanukovych and his last backers that Parliament, dominated by the governing Party of Regions and previously a bastion of loyal support, had given up on him.

“This was the moment that Yanukovych realized that he no longer had even Parliament on his side,” she said, adding that the president had no choice after this but to respect its resolution and order security forces off the streets.

But Mykhalo V. Dobkin, a Party of Regions baron who had for years worked closely with Mr. Yanukovych, said the president did not give the order and had no knowledge of it until security forces suddenly vanished.