Latest developments on the Boston Marathon bombings

BOSTON (CNN) -- -- A spokesman for the Massachusetts Office of the Chief Medical Examiner said Tuesday that Tamerlan Tsarnaev's cause of death has been determined. "It doesn't become public record until the decedent remains have been released and the death certificate has been filed," said Terrel Harris.

-- Alleged Boston bomber Dzhokhar Tsarnaev can speak and has been interacting with medical staff, a spokesman for Federal Medical Center Devens said Sunday.

-- Federal agents are looking into possible links between dead Boston Marathon bomb suspect Tamerlan Tsarnaev and William Plotnikov, a Canadian boxer-turned-jihadist killed last year by Russian troops, a source briefed on the investigation said Monday.

-- Plotnikov, 23, died in a firefight with Russian forces in the southwestern republic of Dagestan in July 2012, while Tsarnaev was visiting the region, the source said. Plotnikov, who was born in Russia, had moved as a teenager with his family to Canada. Investigators are looking into whether Tsarnaev was radicalized during the six-month visit.

-- Investigators are also looking into whether Tsarnaev had had contact with an 18-year-old militant, Mahmoud Mansur Nidal, who was killed last May by Russian forces during a gun battle in Makhachkala, which is Dagestan's capital and where Tsarnaev's parents live.

-- Investigators on Monday searched the family home of Tsarnaev's widow, Katherine Russell, in Rhode Island. She and her toddler daughter -- Tamerlan's child -- have been staying with her parents at their home in North Kingstown. Agents took items that included DNA samples. Russell has said she had known nothing about her husband's alleged plan.

-- Female DNA was discovered on a fragment of a pressure-cooker bomb used in the attack, and investigators are trying to determine whose genetic material it is, law enforcement sources told CNN. One of the sources said it could be from anyone who had contact with any of the bomb's components and it does not necessarily implicate anyone.

-- FBI agents have interviewed "Misha," whose name has surfaced in the Boston bombing investigation, in Rhode Island, a U.S. government official told CNN on Monday. Investigators spoke with the man after members of the suspected bombers' family blamed a "Misha" for radicalizing Tsarnaev.

-- The man, whose real name is Mikhail Allakhverdov, denies having encouraged a violent take on Islam and denies having taught Tamerlan, according to a New York Review of Books writer who says he interviewed Misha.

-- On Monday, a federal judge appointed lawyer Judy Clarke to represent Dzhokhar Tsarnaev, Tamerlan's brother and himself a suspect.

-- After two days of searching a landfill in New Bedford, Massachusetts, investigators have given up trying to find a laptop that could be relevant to the case, a U.S. law enforcement official told CNN on Monday.

-- Russian authorities intercepted a phone call in early 2011 from one of the Tsarnaev brothers in the United States to their mother, Zubeidat Tsarnaev, in Dagestan, an official with knowledge of the investigation told CNN over the weekend. The wiretapped communication discussed jihad, but the conversation was vague, two U.S. officials said. It was unclear why the Russians were eavesdropping on the mother.

-- On Monday, Zubeidat Tsarnaev told CNN's Nick Paton Walsh that she plans to travel to the United States to see her son, despite pending shoplifting charges against her in Massachusetts.