Natalia Estemirova, who has long documented abuses by government-backed militias, is the fourth prominent critic of Kremlin policies to be killed in three years.
From arms control to Afghanistan, analysts say the deals brokered by Obama and Medvedev could profoundly reshape global security.
Since President Obama took office, twice as many Russians report 'positive attitudes' toward the US. But skepticism continues to dominate ties between Washington and the Kremlin.
His administration isn't that interested in a missile shield in Europe, but seems unlikely to concede it in upcoming talks.