The bombings at the Boston Marathon is a grim reminder that an “act of terror” is waiting to happen at anytime, anyplace and targeting anybody.

The worst bombing in the United States since the September 11, 2001, mass killings has claimed the lives thus far of three people and injured more than a 100, both sports persons as well as those cheering for them.

What was initially thought to be surprise fireworks, and accompanied by cheers, soon turned out to be — to the horror of the runners and the onlookers — deadly twin blasts caused by human hands. Then, a screaming frenzy set in.

US President Barack Obama has pledged “to get to the bottom of this” and make those responsible feel “the full weight of justice”.

In a knee-jerk reaction, police on Monday night searched the apartment of a Saudi Arabian youth who was injured in the blast. But yesterday, they relented and law enforcement sources have said the evidence has indicated the Saudi student would be cleared as he did not know anything about the attack.

The killer or killers could in all probability be home-bred. After all, the US has witnessed mass university and school campus killings.

But, what triggers such insensitive and horrifying acts?

Was it in retaliation for last weekend’s incident at the Guantanamo Bay detention camp?

Lurid accounts by inmates of the force-feeding of hunger-strikers may have given cause for extremist reaction, especially as the US is seen as the perpetrator of what goes on in the detention centre.

The inmates, termed as terrorists and many said to be involved in the 9/11 attacks, have been incarcerated without charge or trial for years. Some see no hope of freedom.

The White House has defended the raid on the huger-strikers, but has pointed to the Congress that, it says, has blocked every move to shut down the Guantanamo Bay detention centre.

The US National Security Agency, meanwhile, has denied that a $1.2bn data centre it is building will be used to illegally eavesdrop on or monitor the e-mails of US citizens.

The secretive agency, which serves the US military and intelligence communities, insisted the state-of-the-art facility’s work would be used to support US cybersecurity in accordance with US laws that limit spying on US citizens.

It must be recalled that then president George W Bush had issued an executive order just after 9/11 authorising the NSA to tap phone calls without any need for a warrant.

All in vain, for terror strikes are too sudden, that no amount of preparedness can predict or prevent from happening. Though there have been successes in thwarting mindless killings, the ones that escape notice or scrutiny make the biggest impact.

The annual Boston Marathon, held since 1897, draws more than half a million spectators, with some 20,000 participants, every year.

Though officials in Britain and Spain have said the London and Madrid marathons would go ahead this, security plans have been subjected to review.

As Boston recovers from the senseless violence, the resilience of the people will be put to test. And, as always, they will bounce back with greater strength and the everlasting faith that this will never, ever, happen again.