(NBC NEWS) - One is a medical student described by his father as an angel. The other was a boxer who once said: "I like the USA."
The suspects in the attack on the Boston Marathon — one killed, one on the loose — are brothers of Chechen origin, at least one a legal permanent resident of the United States, law enforcement officials told NBC News.
While authorities were not sure of a motive, NBC News learned that counterterrorism officials were examining possible links between the Boston bombers and the Islamic Jihad Union of central Asia.
The suspect at large early Friday was identified Dzhokhar Tsarnaev, 19, born in Kyrgyzstan, holding a Massachusetts driver's license and living in the Boston suburb of Cambridge. He was the suspect in the white hat in surveillance photos from the marathon released by the FBI.
An account with Dzhokhar Tsarnaev's name on a Russian social media site lists Islam as his world view, "career and money" and his personal priorities and Chechnya as an area of interest.
His father, speaking from Russia, told The Associated Press that he is a second-year medical student and "a true angel."
"He was a nice guy. He was shy," said Sierra Schwartz, who identified herself as a high school friend. "It was almost physically painful to even call him nice now after this absolute tragedy that happened, but at the time, as we knew him, he was funny."
She added that Dzhokhar Tsarnaev never seemed suspicious and that his identification as a suspect in the marathon bombings came as a shock.
Robin Young, who said her nephew was on the wrestling team with him, told NBC News that he was "just a light, airy, curly-haired kid."
"I can't tell you enough what a beautiful young man this was," she said.
The city of Cambridge awarded Dzhokhar Tsarnaev a $2,500 scholarship toward college in 2011, according to The Boston Globe. The scholarships were for students at Cambridge Rindge and Latin School, part of the Cambridge public school system.
Dzhokhar Tsarnaev's brother, who was killed in a firefight with law enforcement, was identified as Tamerlan Tsarnaev, 26, born in Russia. He became a legal permanent resident in 2007, the officials said. He was the suspect in the black hat in the FBI photos.
Tamerlan Tsarnaev boxed in a 2004 tournament as part of Golden Gloves, a charity program, according to The Lowell Sun newspaper. He told the newspaper then: "I like the USA."
He said that his first love was music, and that he played the piano and violin.
"America has a lot of jobs," he said. "That's something Russia doesn't have. You have a chance to make money here if you are willing to work."
Both men were believed to have military experience, and to have entered the country with their family in 2002 or 2003, when the family sought asylum. The nature of the military experience was not clear. Later in the morning, U.S. Army officials told NBC knows that no one matching either name had served in the active-duty Army, or the reserves.
Chechnya is a predominantly Muslim part of Russia with a turbulent history. It declared independence in 1991, after the breakup of the Soviet Union. Chechnya fought war with Russia for much of the 1990s, and Chechens have been involved in terrorist attacks in Russia in the years since.
In 2002, Chechen militants seized a Moscow theater and held 800 people hostage for two days. Special forces raided the building and killed 41 hostage-takers; 129 hostages were killed, mostly from gas used by Russian forces.
In 2004, Chechen insurgents took hundreds of hostages in the Russian town of Beslan. The siege came to a bloody end two days later, and 330 people, about half children, were killed.
Tamerlan Tsarnaev was killed after a chaotic chase and firefight with police early Friday. Authorities were conducting a house-to-house search in the Boston suburb of Watertown for his brother, who was considered armed and extremely dangerous. Massachusetts Gov. Deval Patrick ordered people in Boston and some suburbs to stay inside.