A delegation from the U.S. Embassy in Moscow left for Dagestan on Tuesday as part of the investigation into the Boston Marathon bombings, an embassy official told CNN's Phil Black on Wednesday.
Officials will try to interview the parents of Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev, the official said.
The Russian government is cooperating with the FBI in its investigation, the official added.
The Tsarnaev family is from the Russian republic of Chechnya and fled the brutal wars there in the 1990s. The two brothers were born in Kyrgyzstan; Dzhokhar became a U.S. citizen in 2012, and brother was a legal U.S. resident. Their parents live in Dagestan.
Meanwhile, Dzhokhar Tsarnaev -- the surviving suspect -- has cited the U.S. wars in Afghanistan and Iraq as motivating factors behind last week's attack, a U.S. government official said Tuesday.
Dzhokhar Tsarnaev has been able to communicate with investigators in a limited fashion from his hospital bed and told them that neither he nor his brother Tamerlan, had any contact with terrorist groups overseas. But the official cautioned that the interviews were preliminary, and that Tsarnaev's account needs to be checked out.
The 19-year-old has told investigators the brothers were self-radicalized via the Internet. Investigators also are looking into whether the online English-language magazine Inspire, put out by Al Qaeda in the Arabian Peninsula, was used for instruction on how to make the bombs, but another source cautioned that other outlets could have provided that information.
Nine days after Boylston Street turned into a bloody scene of carnage, the area reopened to public foot traffic Wednesday.
It's another sign Boston is recovering from the twin bombings that killed three and wounded hundreds more.
Also Wednesday, mourners will gather to honor Massachusetts Institute of Technology Officer Sean Collier, who authorities say was fatally shot by the suspected bombers last week. The memorial service will take place on the MIT campus.
And as more details slowly emerge from the bedridden suspect, U.S. officials were traveling to Dagestan to interview the parents of the suspected bombers.
New details on officer's slaying
Collier was killed Thursday night, near the beginning of a wild 24 hours that culminated in Tamerlan Tsarnaev's death and Dzhokhar Tsarnaev's capture in the backyard of a home in the suburb of Watertown, a Boston suburb.
Collier didn't even have time to activate his emergency alert before being shot four or five times in the chest and head as he sat in his patrol car on the MIT campus, according to a source with direct knowledge of the investigation.
It's not clear why the brothers allegedly ambushed the officer, the source said.
Suspect shopped at fireworks store
More than two months before the marathon bombings, Tamerlan Tsarnaev bought two reloadable mortar style fireworks from a New Hampshire store.
On February 6, Tsarnaev had one question for a store assistant at Phantom Fireworks in Seabrook, New Hampshire: "What's the biggest and loudest thing you have?"
After that, store Vice President William Weimer said, Tsarnaev shelled out $200 cash for two "lock and load kits."
Weimer said such behavior is very common in the store. He said the store notified the FBI after discovering that the marathon bombing suspect had bought explosives there.
Law enforcement officials told CNN earlier Tuesday that the number of fireworks bought at the store was not enough to set off explosions the size of those at the Boston Marathon.
"My assumption is they bought this, experimented with it and decided against it and moved on and found another source," Weimer said.
Suspects' family "devastated" by bombings
In a statement issued through their lawyers Tuesday, the suspects' sisters -- Ailina and Bella Tsarnaev -- said they were saddened "to see so many innocent people hurt after such a callous act."
"As a family, we are absolutely devastated by the sense of loss and sorrow this has caused," they said. "We don't have any answers but we look forward to a thorough investigation and hope to learn more."
And Tamerlan Tsarnaev's wife, Katherine Russell, issued a statement through her attorney's office saying she is "doing everything she can to assist with the investigation" and said she and her family are shocked and distraught.
"The reports of involvement by her husband and brother-in-law came as an absolute shock to them all," the statement said.
The suspects' mother, Zubeidat Tsarnaev, said Tuesday that she believed her sons had been framed.
Speaking from her home in Dagestan -- a Russian republic on the Caspian Sea -- Tsarnaev said she thinks her older son died because he was a Muslim and charged that authorities silenced her younger son to prevent him from defending himself.
She said family members have arranged for Tamerlan Tsarnaev to be buried at a mosque in Cambridge, Massachusetts, this week.
CNN's Jake Tapper, Julia Talanova, Carol Cratty,
Brian Vitagliano, Laura Ly, Deborah Feyerick, Nick Paton Walsh, Julian Cummings, Barbara Starr, Susan Candiotti, Jessica Yellin and Joe Johns contributed to this report.