LONDON — The two assassins sent to southwest England in March to poison a Russian former spy were active officers in Russia’s military intelligence, Prime Minister Theresa May of Britain said on Wednesday, after prosecutors accused the men of attempted murder, the first criminal charges in a case that has driven a deep wedge between Russia and the West.

Investigators released a cache of evidence in the case, including security camera images that captured the progress of two husky men from an Aeroflot flight to the scene of the crime, near the victim’s home, and from there back to Moscow.

They also released photographs of the delicate perfume bottle that was used to carry a weapons-grade nerve agent, known as Novichok, to the quiet English cathedral city of Salisbury.

British counterterrorism police said at a news conference that they had pored through thousands of hours of security-camera footage, cross-referenced the results with passport data, and on May 2, identified a shabby hotel in East London where the men had stayed. Finally, in a needle-in-a-haystack moment, two swabs taken from the suspects’ hotel were found to contain traces of the nerve agent.