Updated

Officials across multiple federal agencies failed to take steps to investigate warning signs they had received since 2011 about Boston Marathon bomber Tamerlan Tsarnaev, the intelligence agencies' inspectors general report revealed Thursday.

The findings, released in an unclassified summary of the classified report, highlighted instances where information sharing among 17 federal agencies may have been required in Tsarnaev’s case and where the FBI could have been more vigilant in its investigation of him before the 2013 attack, which killed three and injured over 200.

It cautioned it is impossible to know whether increased measures would have yielded information that could have prevented the attack, and found for the most part the agencies followed procedure appropriately.

One example cited is that the FBI Legal Attaché in Moscow did not coordinate with the CIA after it received information about Tsarnaev from the Russian government in March 2011. Russia informed the FBI that Tsarnaev and his mother Zubeidat practiced radical Islam and that Tamerlan Tsarnaev was planning to travel to Russia to join “bandit underground groups” in Dagestan and Chechnya.

After investigating this information, the report states the FBI closed the probe of Tsarnaev because the agency found no links between him and terrorism. To determine this, an FBI special agent interviewed Tsarnaev and his parents, conducted “drive-bys” of his home and reviewed references to him in other counterterrorism cases.

However, the DOJ inspector general notes that the agent did not use several investigative tactics, including contacting local law enforcement about Tsarnaev or speaking with his wife. He also never interviewed the girlfriend Tsarnaev had been arrested for assaulting in 2009.

The Russians subsequently provided nearly identical information to the CIA in September of that year, the report states, which led to Tsarnaev being placed on a terrorist watchlist. Despite this distinction, the report found that when Tsarnaev did travel to Russia in 2012, his trip was not investigated.

The report states that although a U.S. Customs and Border Patrol agent noted that Tsarnaev had been placed on the watchlist, Tsarnaev’s Russia trip did not result in additional vetting at the airport. It also did not lead to additional investigative steps to determine whether he posed a threat to national security.

FBI agents differed on the significance of the trip, and whether it should have been probed further. One counterterrorism agent told investigators he would not have done anything differently had he learned about Tsarnaev’s travel at the time, because the FBI probe had already been closed.

However, other FBI officials disagreed. One told the watchdog that he did not know about Tsarnaev’s trip until after the bombings, and had he had known he would have ordered a second investigation into Tsarnaev and interviewed him upon his return to the U.S.

An official with Boston's Joint Terrorism Task Force agreed, telling the watchdog if counterterrorism agents had been notified of the trip it would have “changed everything.” She agreed that she believed the FBI would have opened a second probe into Tsarnaev.

Ultimately however, the report found that for the most part federal agencies shared information about and followed procedure regarding Tsarnaev appropriately. It also said the FBI investigation into Tsarnaev was appropriate, considering what the agency knew at the time.

It states that broader information sharing could have been helpful to the investigation, and that the agencies should consider being more proactive in information sharing in the future in certain areas.

The report also states that Russia withheld some information from the U.S. about Tsarnaev, despite its initial flagging of him in 2011. The report did not address specifics.

Tsarnaev died following a shootout and a police chase a few days after the bombings. His alleged accomplice, his younger brother Dzhokhar, has pleaded not guilty to 30 federal charges, including using a weapon of mass destruction.