The brothers who set off two bombs at the Boston Marathon this week were Muslims from the Caucasus area, near Chechnya. Not much is publicly known yet, however, about their motives for attacking innocent Americans. Nor is it known if they acted alone or were part of a larger network.

The brothers were Russian-born, hailing from the Chechnyan region, and lived with their family in various parts of Russia’s North Caucasus. They briefly attended school in Makhachkala, Dagestan, and ended up in Massachusetts after moving to the United States in the early 2000s – reportedly receiving refugee status.

News agencies quoted by Forbes reported that the older brother, Tamerlan, was questioned in the past by the FBI for ties with Chechen extremists per request of the Russian government, but no incriminating information was found and he was let go.  He reportedly spent about seven months visiting Russia in 2012.

The Associated Press located the two terrorist’s father Saturday in Makhachkala.

After moving to the U.S., both men grew up on Norfolk Street in Cambridge, Mass., not far from the main campus of Harvard University and the Massachusetts Institute of Technology, where a campus police officer was shot to death last night. Neighbors said the boys used to play soccer in the street and their father worked on fixing cars behind the family house.

TIME located an online photo essay in which Tamerlan wrote — “I don’t have a single American friend.” By contrast, Dzhokhar appears to have been “a happy, well-adjusted and rather normal teenager, evident in part from his social-media footprint.”

However, TIME wrote, “he also apparently expressed interest in Islamic political causes, including the armed Syrian rebellion and the cause of Chechen independence.”

Reuters quoted Ramzan Kadyrov, Chechnya’s president, as saying: “They grew up and studied in the United States and their attitudes and beliefs were formed there. Any attempt to make a connection between Chechnya and the Tsarnaevs is in vain.”