The Russian government warned the United States twice that alleged Boston Marathon bomber Tamerlan Tsarnaev was a potential terror suspect, but an upcoming Congressional report states he escaped detainment due in part to a spelling error.

According to NBC News, a yet-to-be-released report by the House Homeland Security Committee found that after two notes on Tsarnaev were placed into US security databases, he was able to travel to and from Dagestan – where he allegedly received jihad training for six months – without being detained for questioning.

One of the notes had expired by the time Tsarnaev returned to the United States in July 2012, but another was still active, meaning the warning on his file should’ve brought about his detainment. The report states his name was misspelled with a “y,” however – “Tsarnayev” instead of “Tsarnaev” – and as a result, he was able to come and go without objection.

“This sounds like a huge hole and an opportunity missed,” Ed Davis, the former chief of police in Boston at the time of the bombing, told NBC.

The news outlet states it was able to review copies of the report and the documents that contributed to it, and has laid out the timeline of events like so: In March 2011, the Russian intelligence agency FSB sent the FBI a cable relaying its knowledge of Tsarnaev’s potential links to radical Islamic groups.

After receiving this information, the FBI opened an investigation into Tsarnaev that month, interviewing him in person, but not running surveillance since the case did not reach the required threshold necessary to authorize such action. A note on Tsarnaev was also entered into the TECS security database, which would alert officials every time he left or arrived on US soil.

Finding no links to terrorism, however, the report apparently states the investigation was closed in June.

In September 2011, meanwhile, a second cable was sent by the FSB to officials at the CIA, repeating much of what it told the FBI six months earlier. Although there are no signs that a second investigation was conducted, or that the first one was reopened, NBC quotes unnamed sources who say a second note was placed in the TECS database, but this time the name was misspelled.

According to the note, if Tsarnaev was seen leaving or re-entering the United States, his detention was “mandatory.”

“Detain isolated and immediately call the lookout duty officer at NTC (24X7),” the note read. “Call is mandatory whether or not the officer believes there is an exact match. Advise the person answering the phone that you have a code tip lookout intercept.”

When Tsarnaev originally left New York on a flight to Moscow, he was flagged by the system but not detained, with sources telling NBC that others on the 100-strong “Hot List” of names traveling through JFK airport that day were a higher priority.

By the time Tsarnaev returned to the US in July 2012, the first alert had expired, and the second one did not spring into effect due to the spelling error.

On April 15, 2013, the Boston Marathon bombing killed three individuals and injured more than 260 others. As law enforcement officials hunted down its suspects – Tsarnaev along with his brother Dzhokhar – Tamerlan was killed in a confrontation with police, while Dzhokhar was found in a boat and arrested the next day.

Dzhokhar is pleading not guilty to charges of terrorism related to the bombing, and his trial is scheduled to begin in November.