CIUDAD JUAREZ, Mexico (AP) — Pointing their rifles, Mexican security forces chased away U.S. authorities investigating the shooting of a 15-year-old Mexican by a U.S. Border Patrol agent on the banks of the Rio Grande, the FBI and witnesses told The Associated Press on Wednesday.

The killing of the Mexican by U.S. authorities — the second in less than two weeks — has exposed the distrust between the two countries that lies just below the surface, and has enraged Mexicans who see the death of the boy on Mexican soil as an act of murder.

Shortly after the boy was shot, Mexican soldiers arrived at the scene and pointed their guns at the Border Patrol agents across the riverbank while bystanders screamed insults and hurled rocks and firecrackers, FBI spokeswoman Andrea Simmons said. She said the agents were forced to withdraw.

"It pretty quickly got very intense over on the Mexican side," she said, adding that FBI agents showed up later and resumed the investigation, even as Mexican authorities pointed guns at them from across the river....

A U.S. official close to the investigation told the AP that authorities have a video showing that the Border Patrol agent did not cross into Mexico. In fact, the official said, the video shows what appear to be members of Mexican law enforcement crossing onto the U.S. side, picking something up and returning to Mexico. The official was not cleared to speak about the video and spoke only on condition of anonymity.

Alejandro Pariente, Chihuahua state's regional deputy attorney general, said the U.S. Border Patrol has given him video which he is reviewing. He declined to describe it except to say that it has sped up the investigation.

The two killings have provoked anger in Mexico like no other recent controversy surrounding immigration, including Arizona's new law making it a state crime to be an illegal immigrant and President Obama's decision to send the National Guard to the border.

Although many Mexicans were unhappy with both initiatives, popular and official reaction had been subdued, in contrast to street protests seen in previous years when the U.S. has cracked down on the border. Many Mexicans have since given up hope for a quick solution to the immigration problem, while other issues including growing drug violence have taken center stage in relations between the two countries.

The two killings have provoked anger in Mexico like no other recent controversy.....

It seems to me that if the young man died on Mexican soil then it is Mexico's right and responsibility to investigate the killing.

The Border Patrol was collecting evidence on the US side to determine if the border patrol accused of killing the young man had crossed over into Mexico.

That investigation should not be interfered with by Mexican troops.

Lucky for the Mexican troops we have a liberal in the WH that wont authorize return fire without higher approval.

IMO, our troops should have the right to return fire, call in air assistance and feel quite secure about investigating alleged crimes on OUR soil.

Yeah great campaign that was...the (censored) retaliation for us burning down Toronto (then York)...and we actually did some real damage, unlike the panzy Brits who left 26 hours after arriving in Washington...they ran away from, a tornado which itself would have done just as much damage! In doing so, they made sure of their failure to invade New York, because they diverted men and ships to Washington for a pointless raid...a mere act of retaliation

The Border Patrol was collecting evidence on the US side to determine if the border patrol accused of killing the young man had crossed over into Mexico.

Yeah great campaign that was...the (censored) retaliation for us burning down Toronto (then York)...and we actually did some real damage, unlike the panzy Brits who left 26 hours after arriving in Washington...they ran away from, a tornado which itself would have done just as much damage! In doing so, they made sure of their failure to invade New York, because they diverted men and ships to Washington for a pointless raid...a mere act of retaliation

We kicked yer butt.

Get over it.

Give us open borders.

You guys didn't exist then. We kicked the British arse, not the other way around. Remember we burnt down Toronto. The escapade into Washington was actually harmful to the British war effort, and, took ZERO American causalities. It was against the code of war and nothing more then juvenile vandalism

It's not their job to investigate themselves. Since the young man died in Mexico, it is Mexico's job to investigate, even if that means crossing the border to gather evidence or interviewing men on the U.S border patrol. But of course we're the U.S. so we'll do what we want and tell Mexico what we found out later.

The Mexican authorities have no more legal or moral right to enter the US without permission than American authorities have to enter Mexico without permission

It's not their job to investigate themselves. Since the young man died in Mexico, it is Mexico's job to investigate, even if that means crossing the border to gather evidence or interviewing men on the U.S border patrol. But of course we're the U.S. so we'll do what we want and tell Mexico what we found out later.

Yeah great campaign that was...the (censored) retaliation for us burning down Toronto (then York)...and we actually did some real damage, unlike the panzy Brits who left 26 hours after arriving in Washington...they ran away from, a tornado which itself would have done just as much damage! In doing so, they made sure of their failure to invade New York, because they diverted men and ships to Washington for a pointless raid...a mere act of retaliation

You guys didn't exist then. We kicked the British arse, not the other way around. Remember we burnt down Toronto. The escapade into Washington was actually harmful to the British war effort, and, took ZERO American causalities. It was against the code of war and nothing more then juvenile vandalism

We started the war, had no material gains, achieved none of our war aims, and took immense damage via blockade and raids, I scarcely think we can say that we kicked the British arse