The Saudi military student who shot and killed three sailors and wounded eight other people on a U.S. Navy base in Florida last week became a Muslim extremist long before he came to the United States, according to a Saudi Arabian government report.

But he went unnoticed for years.

The internal report, obtained by the Washington Post, says “a Twitter account believed to have been used by Ahmed Mohammed al-Shamrani indicates that four religious figures described as radical appear to have shaped the Saudi Air Force trainee’s ‘extremist thought.’”

The terror attack last Friday at Naval Air Station Pensacola — where thousands of American and foreign service members go for training — “has raised concerns about the vetting of foreign military personnel who take part in training and exchange programs in the United States,” the Post says.

The Pentagon acted on those concerns on Tuesday by suspending training for about 850 Saudi students.

Officials have scrambled to piece together limited information about Shamrani, who arrived in the United States in 2017 as part of an extended program to become a weapons systems operator,” the Post says. Shamrani, 21, was killed by a sheriff’s deputy after opening fire in a classroom.

The Saudi report offers a likely reason why Samrani’s Twitter activity went undetected: the account was not under his full name, “but rather parts of his name that are common in Saudi Arabia, and contained no biographical information or photo.”

It notes that Shamrani is the name of one of the kingdom’s largest tribes and “it is not uncommon for extremists and terrorists to use [the] pseudonym of a large tribe to hide their real identity on social media.”

Shortly before Shamrani’s attack, a “manifesto” appeared on his feed denouncing “crimes against Muslims,” the presence of U.S. forces in Muslim countries, the terrorist prison at Guantánamo Bay, Cuba, and U.S. support for Israel.

But evidence of Samrani’s radicalization first appeared on Twitter four years ago, when he was attracted to the jihadist teachings of four men influential in the Muslim world, including two Saudi nationals who were arrested by the Saudi government in 2016.