Katherine Russell, wife of Boston Marathon bomber suspect Tamerlan Tsarnaev, leaves the law office of DeLuca and Weizenbaum in Providence, R.I., on April 29. (Stew Milne/AP)

Federal law enforcement officials are sharpening their focus on the widow of the dead suspect in the Boston Marathon bombing after finding al-Qaeda’s Inspire magazine and other radical Islamist material on her computer, according to law enforcement officials.

The probe of the computer belonging to Katherine Russell, 24, widow of Tamerlan Tsarnaev, is part of the effort by investigators to determine whether Russell knew anything about the April 15 bombing plot or helped her husband and his brother, Dzhokhar, hide from authorities, according to the officials, who spoke on the condition of anonymity to discuss the ongoing investigation.

Officials have concluded that fingerprints and female DNA found on fragments of the pressure-cooker bombs do not match Russell’s, but they say they are continuing to investigate.

Dzhokhar Tsarnaev, 19, the surviving suspect, has told investigators that he and his brother learned to build the bombs from an English-language Inspire magazine and that they were partly influenced by the online sermons of Anwar al-Awlaki, an al-Qaeda propagandist who was killed by a U.S. drone strike in Yemen in 2011.

According to officials, Dzho­khar Tsarnaev also told investigators that he and his brother built the bombs in Tamerlan Tsarnaev’s apartment in Cambridge, Mass., where the elder brother lived with Russell and their daughter. Officials said that Russell called her husband when she saw his photograph on television — following the FBI’s release of the pictures of the suspects — but did not notify authorities.

One of the key questions for investigators is whether the radical Islamist materials on Russell’s computer belonged to her or were downloaded by her husband or someone else.

Russell’s attorney, Amato DeLuca, did not return phone calls seeking comment.

DeLuca had previously said his client played no role in the plot and was shocked to learn of the involvement of her husband and brother-in-law.

Tamerlan Tsarnaev, who was killed during a confrontation with police four days after the bombing, died from gunshot wounds and blunt trauma to his head and torso, according to Peter Stefan, the funeral home owner who is preparing his body for burial. Stefan read details from the death certificate, which lists Tsarnaev’s time of death as 1:35 a.m. on April 19, the Associated Press reported. During the gunfight, Dzhokhar Tsarnaev, driving a stolen sport-utility vehicle, ran over his brother and dragged his body under the vehicle.

In another development, federal agents, state troopers and local law enforcement officers scoured a wooded area near Dartmouth, Mass., where Dzho­khar Tsarnaev attended college. Investigators are looking for evidence that might indicate the brothers tested explosives there, according to a law enforcement official. People who live nearby reported hearing loud noises coming from the woods on March 30.

Jason J. Pack, an FBI spokesman, said the Dartmouth search, in which explosives-sniffing dogs were used, was part of the continuing investigation into the bombings.

On Monday, FBI special agents spent about 90 minutes inside the North Kingstown, R.I., home of Russell’s parents, where she has been staying.

Law enforcement officials said several “persons of interest” in the United States and Russia are being investigated in connection with the brothers. One of the primary focuses remains the seven months that Tamerlan Tsarnaev spent in strife-torn regions of southern Russia last year.

During 16 hours of questioning in the hospital by the FBI, the younger Tsarnaev told agents that he and his brother initially considered carrying out suicide bombings and executing their plot on the Fourth of July at Boston’s large celebration along the Charles River, two law enforcement officials said.

But Tsarnaev said that he and his brother decided to launch their attack earlier because they were able to assemble the bombs in three or four days, more quickly than they had expected, according to two law enforcement officials.

Officials have expressed skepticism about Tsarnaev’s account, saying that the complexity of the bombs makes it unlikely that the brothers could have completed them as fast as he claimed.

According to a government document obtained by NBC News, a detailed analysis of the bombs used at the Boston Marathon and pipe bombs allegedly thrown at police from a car by the Tsarnaevs during a gunfight four days later show striking similarities to instructions from Inspire magazine.

The report from the Terrorist Explosive Device Analytical Center said that the design of the pressure-cooker bombs and the pipe bombs resembled instructions provided in an article in the first issue of Inspire headlined “Make a Bomb in the Kitchen of Your Mom.”

The pressure-cooker bombs had different triggers and power sources than the Inspire designs, but they matched the magazine instructions in the use of several components, including gunpowder from fireworks, according to the TEDAC analysis.