Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev befriended a brain-damaged anti-U.S. government conspiracy theorist through their mother's health care aide job years before the deadly attack, a lawyer said Tuesday. 
 
 Attorney Jason Rosenberg, who represents the family of Donald Larking, said Larking shared publications with the brothers, especially Tamerlan, and discussed theories including that the Sept. 11, 2001, terror attacks and the Newtown, Connecticut, elementary school shooting didn't happen or the U.S. government was behind them. 
 
 The attorney said the Tsarnaev family had a relationship with the Larkings that started years ago when the brothers' mother began working as a personal care assistant for Larking's wife, a quadriplegic since birth. 
 
 Rosenberg said Larking, who lives in West Newton, just west of Boston, was shot in the head in 1974 in an attempted robbery while working in a convenience store. He said Larking suffered brain damage that led to problems with his decision-making and judgment. 
 
 Authorities say the Tsarnaev brothers orchestrated the April 15 marathon bombing, in which two pressure cookers loaded with shrapnel exploded near the race's finish line, killing three people and injuring more than 260 others. Dzhokhar Tsarnaev pleaded not guilty last month to charges including using a weapon of mass destruction to kill. Tamerlan Tsarnaev died after a shootout with police a few days after the bombing. 
 
 Rosenberg said Tuesday the Tsarnaev brothers got to know Larking while substituting for their mother sometimes by helping to care for his wife. The attorney said the brothers "were very helpful, very kind" to the couple and Larking shared his views with them as he found anti-U.S. government websites and became angrier and irrational. 
 
 The attorney said Larking, who has many Jewish friends, also has literature that questions if the Holocaust happened. 
 
 The lawyer's account first emerged in a Wall Street Journal article, which included Tamerlan Tsarnaev's former landlady talking about publications that had been in his Cambridge apartment. 
 
 Landlady Joanna Herlihy told The Associated Press she salvaged publications after authorities had finished searching the apartment and items were discarded. She confirmed that among them were an Alabama-based publication that uses a Confederate flag on its website and a weekly publication that the Southern Poverty Law Center calls anti-Semitic. 
 
 Rosenberg said Tuesday he doesn't think Larking helped the Tsarnaev brothers, ethnic Chechens from Russia, formulate ideas but may have made them believe others felt as they did. 
 
 "(They) were seeing someone who was Caucasian and was born in America who was saying the same things," the attorney said. 
 
 Rosenberg said he doesn't know if the Tsarnaev brothers understood how seriously Larking's brain was affected from the long-ago shooting. He said he's talked to Larking since the Boston Marathon bombing but doesn't think his friend comprehends what happened. 
 
 The brothers took Larking to their mosque, and he converted to Islam and still attends the mosque, Rosenberg said. 
 
 Larking seemed close to Tamerlan, and Tamerlan made sure to help Larking, who wears braces on his legs, when they attended the mosque together, said Nicole Mossalam, a spokeswoman for the Islamic Society of Boston mosque in Cambridge. 
 
 Mossalam said it becomes obvious during conversation that Larking has a disability because he's unusually open and "childlike" and often says politically incorrect things without seeming to realize it. 
 
 "He loves to sit down with people and talk, and there's basically no filter," she said. 
 
 In a federal indictment in June, authorities alleged they found on Dzhokhar Tsarnaev's computer a publication written by someone known as the Father of Global Jihad that advocates violence to terrorize Islam's perceived enemies. 
 
 Prosecutors also alleged he downloaded an article from a publication that "glorifies martyrdom in the service of violent jihad" and a magazine that had directions for building bombs using pressure cookers. ||||| Lawyers for accused Boston Marathon bomber Dzhokhar Tsarnaev asserted Friday that his older brother and alleged accomplice had been encouraged by the FBI to be an informant and to report on the Chechen and Muslim community, according to court records. 
 
 “We seek this information based on our belief that these contacts were among the precipitating events for Tamerlan’s actions during the week of April 15, 2013, and thus material to the defense case in mitigation,” the lawyers said in their court filing. 
 
 “We base this on information from our client’s family and other sources that the FBI made more than one visit to talk with Anzor [his father], Zubeidat [his mother] and Tamerlan, questioned Tamerlan about his Internet searches, and asked him to be an informant, reporting on the Chechen and Muslim community. 
 
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 “We do not suggest that these contacts are to be blamed and have no evidence to suggest that they were improper, but rather view them as an important part of the story of Tamerlan’s decline. Since Tamerlan is dead, the government is the source of corroboration that these visits did in fact occur and of what was said during them.” 
 
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 The lawyers suggested that Tamerlan Tsarnaev could have misinterpreted his interactions with the FBI as pressure from the agency, and that they could have “increased his paranoia and distress.” 
 
 The defense wants to investigate those factors as it seeks to portray Tamerlan as a dominating family figure who may have pushed the younger Dzhokhar to take part in the April 15 bombings last year. Tamerlan was killed days after the bombings in a confrontation with police in Watertown. 
 
 The lawyers’ allegation, based on conversations with family members and other sources, was made in a 23-page court filing Friday in which the lawyers sought a court order forcing prosecutors to turn over more evidence in the case. 
 
 Specifically, they want additional evidence about Tamerlan’s radical views, which would be useful in the lawyers’ defense against the death penalty. 
 
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 Lawyers argued that, now that prosecutors have declared they will seek capital punishment, Dzhokar should be allowed to present evidence of mitigating factors that would tilt a jury against the death penalty. 
 
 Those factors include evidence about his age at the time of the bombings, which was 19, his lack of criminal history, and the possible influence of others, specifically a radical older brother, court records said. 
 
 “The underlying data concerning the brothers’ activities, state of mind, and respective trajectories is critical,” the defense said. “Evidence that shows Tamerlan to have had a substantially longer and deeper engagement than his younger brother with extremist and violent ideology is mitigating for the light that it sheds on their relative culpability.” 
 
 Prosecutors did not immediately respond to the defense request, though defense lawyers conceded that they have a March 14, 2014, letter in which prosecutors said they had “no evidence that Tamerlan Tsarnaev was solicited by the government to be an informant.” 
 
 Although the FBI does not comment on court matters, the bureau cited a statement Friday that it made Oct. 18, 2013, which said, “The Tsarnaev brothers were never sources for the FBI, nor did the FBI attempt to recruit them as sources.” 
 
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 Dzokhar Tsarnaev, now 20, faces a 30-count indictment in his alleged role in the bombings, which killed three people and injured more than 260. He and Tamerlan also allegedly shot and killed an MIT police officer before the confrontation with police in Watertown. 
 
 Tsarnaev is being held at the federal prison at Fort Devens in Ayer. He is slated to go to trial in November. 
 
 Prosecutors have described him as a young Muslim extremist who wanted to carry out jihad, or holy war, against the United States. They alleged the brothers learned to build the bombs through websites that supported Al Qaeda. 
 
 In court requests filed late Friday, the defense lawyers sought a court order to force prosecutors to turn over a list of records, including reports related to the fatal shooting of MIT police Officer Sean Collier, the Watertown confrontation, and any evidence that an MBTA police officer was shot by fellow officers, rather than by Dzokhar Tsarnaev, who the lawyers say was unarmed. 
 
 The request also targets records of the brothers’ Internet searches. 
 
 One of the court requests asked for any information prosecutors collected under the Foreign Intelligence Surveillance Act including any surveillance of Tamerlan’s return visits to Dagestan and the Chechnya region before the bombings. 
 
 A recent US House of Representatives homeland security report indicated FBI officials in Moscow may have collected “electronic communication” between Tamerlan and a jihadist named William Plotnikov. 
 
 “Any surveillance, evidence, or interviews showing that Tamerlan’s pursuit of jihad predated Dzhokhar’s would tend to support the theory that Tamerlan was the main instigator of the tragic events that followed,” the defense lawyers argued. 
 
 The lawyers are also seeking the immigration records of Tsarnaev’s family members, including his mother, father, and brother. 
 
 His father, Anzor, sought the family’s asylum in fleeing torture in Kyrgyzstan close to two decades ago, and the defense lawyers argued that the records would illustrate Tsarnaev’s family history. 
 
 They also said that Tamerlan’s immigration records could yield more evidence about his encounters with federal authorities, specifically after his visits to Dagestan that caught the attention of Russian officials. 
 
 The lawyers said they plan to argue that the unknowns about Tsarnaev’s “formative environment and relative moral culpability” and the possible “psychological domination” by his brother would support their case against the death penalty. 
 
 Globe correspondent Haven Orecchio-Egresitz contributed to this report. Milton J. Valencia can be reached at MValencia@globe.com.
– Did a brain-damaged American help turn the Boston bombing suspects against the US? The far-right and conspiracy theorist publications found in Tamerlan Tsarnaev's apartment appear to have been supplied by an elderly man befriended by the brothers through their mother's job as a home health aide, the Wall Street Journal finds. A lawyer for the family of Donald Larking, a 67-year-old who suffered brain damage when he was shot in a robbery 40 years ago, says Larking was obsessed with conspiracy theories and shared publications with the brothers that questioned the Holocaust and accused the US or Israeli governments of being behind 9/11 and the Newtown school shooting. Larking also supplied the brothers with copies of a white supremacist newspaper published in Alabama. He became so close to Tamerlan that he converted to Islam and began attending the local mosque with him, says the lawyer, who stresses that the shooting badly impaired the elderly man's "awareness of the realities of the world" and his ability to make decisions, the AP reports. Larking, who still attends the mosque, has sunk into "depression and anger" since the Boston Marathon bombing and believes his friends were the victims of another conspiracy, the lawyer says.