Being linked to a loud noise in Mexico could lead to terrorism charges.

This is a country, after all, traumatized by drug violence.

That is why a crowd in northern Mexico was sent into panicked stampede when the exhaust pipes of two motorcycles backfired, sounding a lot like gunshots. Now the two motorcyclists are facing terrorism charges.

It was the second time in less than a year that people have been charged in Mexico under terrorism statutes for spooking the populace in areas of the country hit by drug violence. Officials say state criminal codes often lack lesser but more appropriate charges to handle situations involving acts that may be irresponsible but are hardly criminal.

The two motorcyclists, Juan Ramon Munguia and Enrique Trevino Rívera, were leaving their workplace Saturday evening at a store near the main square of the northern city of San Luis Potosi, where an Easter week festival was being held.

The two got on their bikes and fired them up, and that is when the confusion began.

"There are two versions: They (the motorcyclists) say that is just where they usually warm up their engines," said San Luis Potosi state spokesman Juan Antonio Hernández. "But there are witnesses who say they purposely continued to rev their engines , even after people had started to panic."

Because the backfiring of the engines sounded like the popping of gunshots, hundreds of people in the main square who were celebrating a Holy Week event that involves the burning of paper-mache figures representing villains started to stampede out of the square, seeking cover.

But the streets were nearly blocked by vendor stalls selling traditional Mexican food, causing the crowd to pile up and resulting in some people getting trampled.

That, not the motorcycle engines, was the real problem, according to the state Human Rights Commission, which said it had launched an investigation into the arrests.

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"There is possible blame that can be attributed to city authorities who allowed vendors to set up stands in the square without the appropriate controls, which prevented a rapid evacuation," the commission said in a statement Wednesday.

"The arrests and charges of terrorism lack any legal basis," according to the statement. "This commission has evidence that the two workers were leaving work and doing what they do every day, starting up a motorcycle they use as transport."

The agency also noted the two suspects said they had been beaten by police after their arrest.

It would all seem like a tempest in a teapot, if the two men weren't facing possible sentences of five to 20 years in prison if convicted. While that seems like harsh punishment for a noisy exhaust, Hernández said such irresponsible behavior is a real problem for states like San Luis Potosi, where drug-gang gunbattles have terrorized residents in recent years.

While the most serious injuries appear to have been bruises or blows from people falling or being stepped on in the crowd, Hernández said that "we were on the threshold of having a tragedy."

Crowds have been sent scrambling for cover at concerts, baseball and soccer games in Mexico when gunfire has broken out nearby in recent years. A grenade attack on an independence day celebration in 2008 killed eight people and wounded dozens in the main square of the Michoacan state capital, Morelia.

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In San Luis Potosi, Hernández said, there have been tens of thousands of fake calls to emergency numbers and bomb threats to a local hospital over the last year.

State law defines terrorism as acts that "produce alarm, terror or fear in the population ... to disturb the public peace or try to undermine government authority."

It is not the first time such charges have been brought in Mexico. In September, two people in the Gulf coast state of Veracruz were charged with terrorism for posting on social networking sites unverified rumors of mass attacks by criminals on the local population.

Following a public outcry, those charges were dropped.

It was unclear whether the two suspects in San Luis Potosi had lawyers, but Claribel Guevara, who served as a defense attorney for the suspects in Veracruz, called the charges unwarranted and disappointing.

"This is even more sad and terrible, that instead of learning (from the Veracruz case), they are committing the same errors and the same violations of human rights," Guevara said, noting that one of her clients suffered health problems and been out of work for about six months following his arrest.

She believes that authorities, who have had limited success in battling drug gangs, instead focus on easier targets — common citizens whose acts sometimes cause panic.

"I think that what is really behind this is that they want to tell the public, 'Here, we are really investigating ... here is the proof that the police are doing their jobs."

After the Veracruz case became a freedom-of-speech issue, that state proposed changing its laws to create something closer to a charge of "disturbing the peace," so as to avoid having to use terrorism charges again.

Hernández said San Luis Potosi is hoping to do the same, but notes authorities are between a rock and a hard place.

"That's the problem, they ask you to apply the law, and when you apply the law, then all sorts of justifications and criticisms come up," he said.

Based on reporting by The Associated Press.

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