May 20, 6:46 PM EDT

A federal judge has found a U.S. Border Patrol agent was justified in the fatal 2011 shooting of a suspect who was caught in the line of fire while fleeing in southern Arizona

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PHOENIX (AP) -- A federal judge has found that a U.S. Border Patrol agent was justified in the 2011 fatal shooting of a suspect who was caught in the line of fire while fleeing in southern Arizona.

Judge James Soto ruled April 25 that agent Lucas Tidwell cannot be held liable for the killing of Douglas resident Carlos LaMadrid because Tidwell was within the law. The Tucson Sentinel reported the ruling this week.

The lawsuit was filed by LaMadrid's mother, Guadalupe Guerrero, in federal court in Tucson. William Risner, her attorney, declined to comment.

Tidwell was represented by the U.S. Attorney's Office in San Diego. U.S. Attorney Laura Duffy of the Southern District of California said LaMadrid's death was a tragic loss of life but that the judge ruled correctly because Tidwell was acting in self-defense.

"As the judge said, a reasonable person would have believed his life was in serious danger when rocks the size of bricks were being thrown at his head," she said in a statement to The Associated Press.

The incident began on March 21, 2011, when Douglas police attempted to pull 19-year-old LaMadrid over after getting a call that he might have drugs in a truck he was driving. LaMadrid fled toward the Mexican border, where two men had propped up a ladder. One of the men helped LaMadrid climb the ladder while the other threw large rocks at Tidwell, police said.

Tidwell fired his weapon after one of the rocks nearly hit him in the head. LaMadrid was caught in the line of fire and killed.

The shooting is one of several in which border agents have fired at rock-throwers, raising concern among civil rights groups who say agents fire indiscriminately.

But the Border Patrol says rocks can cause death and that agents need to use deadly force to defend themselves.

LaMadrid's family says the shooting was reckless, intentional and unwarranted. LaMadrid wasn't armed.

But Soto said Tidwell followed the law in the shooting and could not be held legally liable.

"Whatever decision the court made in this case, it could not begin to fill the immense void left in the family when LaMadrid died," he wrote.

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