US intelligence veterans are warning that mounting criticism of the FBI for not preventing the Boston bombing risks encouraging infringements of civil liberties, such as routine surveillance of mosques and blanket use of security cameras.

Investigators are under pressure to explain how a tip-off from Russian officials in 2011 did not lead to closer scrutiny of bomb suspect Tamerlan Tsarnaev, which might have stopped last week's attack.

White House officials say they are re-examining the first FBI investigation, although they insist it went through Tsarnaev's background thoroughly at the time and found no threat of violence.

The surviving suspect, 19-year-old Dzhokhar Tsarnaev, was charged at his hospital bed on Monday with using and conspiring to use a weapon of mass destruction, a count that carries a possible death penalty. Despite serious injuries to the neck and throat, Tsarnaev was deemed able to communicate. "I find that the defendant is alert, mentally competent and lucid," said the judge, Marianne B Bowler, according to a transcript of the hearing.

Details about the alleged bombers' apparent motivations began to emerge on Tuesday from leaks of the initial questioning of Dzhokhar Tsarnaev. ABC, NBC and the Associated Press reported US officials as saying that preliminary evidence from the younger man's interrogation suggests the brothers were motivated by religious extremism but were apparently not involved with Islamic terrorist organizations.

The AP said Tsarnaev communicated with his interrogators in writing, hindering the type of back-and-forth exchanges that are seen as important to establishing key facts and their meaning. The officials cautioned that they were still trying to verify what they were told and are also looking at the suspect's telephone and online communications.

As questions continued to be asked about what the FBI knew about his older brother Tamerlan, experts close to the intelligence establishment say there is widespread misunderstanding of what it would take to put all tip-offs about radical individuals under close surveillance.

Philip Mudd, a former FBI senior intelligence adviser, said there was a risk of a backlash turning the US into a "surveillance state".

"During daily threat briefings, we would look at homegrowns all the time," he told the Guardian. "The question is: what kind of screening do you want in place to get an American into that lense? Before you want to swing that pendulum too far: be careful."

"If you want to guarantee we find those folks – and by the way, the FBI wouldn't, anyway – there is only so much you can do in a open society to penetrate a closed circle," he added during a debate at the Brookings Institution.

The intelligence community has reacted defensively to the criticism this week of the Boston case, which has been led by Republican politicians such as Michael McCaul, chairman of the House homeland security committee.

Bruce Reidel, a former CIA and Pentagon official now at Brookings, said: "You can pretty much count on anything that happens in the US being labelled an intelligence failure within 24 hours."

He suggested the Boston bombings might instead provoke a reassessment of the dangers of homegrown radicals in the US. "A few years ago we very proudly said we didn't have a problem in the US with radicalised Muslims – that that was a European problem, a British problem," said Reidel.

But Mudd said the criticism from Washington politicians risked dragging the US down a route it did not want to go. "It's such a misunderstanding of how national security operates. If he had not appeared in US government databases what would people have said: you missed it! When you are sitting there at the threat session every day, the threat matrix is a volume business," he said.

"We are going to see this again, and we are going to ask ourselves: how did we fail? But before you ask that question, how are you going to boil the 10,000 people you interview down to that one case, and how are you going to deal with the 500 false positives?"

Mudd, who also served as deputy director of the CIA's counter-terrorism center, said Americans did not have the appetite for the type of routine closed circuit television surveillance seen in cities such as London after the 7/7 attacks.

"Do we spy on mosques? You need to tell me there is someone who is considering an act of violence first," he added. "It is inappropriate to intervene in a religious activity without you telling me that someone in there is doing something wrong."

Mudd also told the Guardian he thought criticism that the FBI was too slow in releasing video images of the Boston suspects was unfair.

Congressman McCaul was less forgiving. He has written to the FBI demanding to know why it "dropped the ball" after the 2011 probe of Tsarnaev.

The White House said it was satisfied with the FBI's account of the 2011 investigation but would be reexamining all aspects of the case. "The FBI thoroughly investigated the information it received, that included checking databases, associations with other people of interest, and travel history," said spokesman Jay Carney.