The Moscow concert massacre was a major security blunder. What's behind that failure?

The Moscow concert hall attack a week ago that left more than 140 people dead was a major blunder for Russia’s law enforcement agencies. While the government register of terrorist and extremist groups in the country includes al-Qaida and the Islamic State group, it also lists LGBTQ+ activists and political opposition groups like that of the late opposition leader Alexei Navalny. That has raised questions about how Russia’s vast security services evaluate threats to the country and how gunmen could easily kill so many people at a public event. President Vladimir Putin came to power 24 years ago by taking a tough line against what he labeled as terrorism.