https://www.wbur.org/radioboston/2017/06/15/tsarnaev-mcphee-fbi
Our investigation begins with a journey. On Jan. 21, 2012, Tsarnaev flew to Russia, 15 months before the Marathon bombing. U.S. Customs and Border Patrol (CBP) agents allowed Tsarnaev to board his flight without any additional screening, even though a year earlier Russian intelligence services had issued specific warnings about Tsarnaev to both the FBI and CIA.
"Those warnings were: Tamerlan is going to come to Russia and join the jihad," McPhee says. "Well, Tamerlan did indeed go to Russia to join the jihad, was there for six months, came back, and breezed through customs despite the fact he was on multiple terror watch lists on this very day."
Tsarnaev was indeed on U.S. terror watch lists. But what exactly was Tsarnaev doing in the Northern Caucasus region of Dagestan from January to July 2012?