It was a family barbecue in a park on the Rio Grande, a belated birthday party for Guillermo Arevalo Pedraza's wife, Nora, and their two daughters, Mariana and Priscila, ages 9 and 10.
Arevalo and his buddy, Josue Gonzalez, were lighting the coals and the girls were playing by the water's edge when they heard the deafening roar of a Border Patrol airboat.
They watched it turn in the fast current and pull beside a man in the river. An agitated crowd soon gathered on the Mexican shore and began shouting at the two agents to let him be.
Gonzalez and Arevalo ran toward the commotion, the girls close behind. Gonzalez could see one of the border agents try to snag the swimmer with a long boat hook.
The agents in the airboat later would report that about 20 people on the Mexican shore began throwing rocks at them. Mexican witnesses would deny it.
What's not in dispute is that an agent dropped to one knee, aimed and fired at least five shots from his M4 carbine. "Good lighting," the agents' report states. "Subject silhouetted."
People screamed and scattered up the riverbank. Gonzalez dived into the tall grass.
Arevalo, a burly 37-year-old bricklayer, was slower.
A bullet hit the rocks, and fragments tore into his left leg. As he went down, another round slammed into his left side, above the pelvis. A third round punctured the right side of his chest.
"Ayudame, ayudame," Arevalo whispered, reaching his hand out before he died. Help me.
More than two years later, the FBI is still investigating the case. The Border Patrol has not given Arevalo's family any explanation of what happened other than a three-sentence statement issued a day after he was killed.
It said agents in a boat were "subjected to rocks being thrown at them" from the Mexican side of the Rio Grande. "A weapon was discharged by Border Patrol," it added. It did not mention any casualties.
A Times investigation — based on the Border Patrol's Use of Force report obtained under the Freedom of Information Act, Mexican autopsy and police records, court documents and interviews with four witnesses — raises questions about whether the agent who fired from the boat overstated the threat from shore, and whether the shooting was justified.
Like other law enforcement officers, Border Patrol agents are only permitted to fire weapons under extreme circumstances — when they have a "reasonable belief" that they face an "imminent danger of serious physical injury or death."
Border Patrol agents fired their weapons in 960 encounters over the last eight years, according to Border Patrol records. Including Arevalo, 30 people were killed, with at least 10 of those in incidents alleged to involve rock-throwing and eight on the Mexican side of the border.
Unlike domestic police departments, the 20,833-member Border Patrol — the federal government's largest law enforcement agency — releases almost no public information about shootings, including the outcome of any investigations.
No one in the Border Patrol has been formally disciplined or fired for any of the deaths or other shooting incidents, according to Mark Morgan, head of internal affairs at Customs and Border Protection, the Border Patrol's parent agency.
Border Patrol defenders say the agency has improved training and given investigators more power to charge agents who violate use-of-force rules.
Until this year, however, agency leaders rejected recommendations to change policies to instruct agents to retreat if possible when people throw rocks, rather than use deadly force.
Critics say more needs to be done to change the agency's insular culture and to improve transparency and accountability for the use of force.
"I don't think [agents] should be shooting people when they're chucking a rock across the border," said Robert Timmel, who was rebuffed when he tried tightening the rules as deputy director of Border Patrol internal affairs from 2008 to 2011. "Common sense tells you to back up."
His superior at the time, James Wong, said he repeatedly asked about the cross-border shootings. "They shot into Mexico? They don't know if they hit anybody? What were they shooting at?" he said.
But he said agency leaders told him he didn't understand the threats agents faced.
"They said we didn't wear green" like agents in the field, Wong said. "'You've never been a Border Patrol agent and you've never been rocked.'"
Bridges between Laredo, Texas, and Nuevo Laredo, Mexico, where Arevalo was shot, are some of the busiest crossings on the border. Civic boosters call the two towns "one city separated by a river."
But Nuevo Laredo has been a battleground for Mexico's most violent gangs. The Sinaloa and Gulf drug cartels have fought a 10-year war against the rival Zetas for access to Interstate 35, the highway that runs from Texas to Michigan and is a major smuggling route.
In May 2012, the height of the war, 23 corpses were found — nine hanging from bridges and 14 decapitated and left at City Hall. Car bombs exploded, a casino and nightclub were firebombed, and a newspaper office was shot up.
The bloodshed has subsided, but downtown still shutters by nightfall and Mexican soldiers patrol the streets. It remains one of Mexico's most dangerous cities.
The cartels help smuggle people north as well as drugs, and the Border Patrol says it has seen more violence as a result.
"Anything that is out there can be used against our agents," said Hector Garza, spokesman for the Laredo local of the border agents union. "Mesquite wood, firearms, rocks, you name it."
Four Border Patrol agents have been killed in the line of duty since 2006. Two were shot to death, one was run over by a suspected smuggler, and one was shot by other agents after he mistakenly opened fire on them.
Agents running the patrol boats on the Rio Grande are particularly exposed, Garza said.
"It's one of the most dangerous spots to be in the Border Patrol," he said. "You're between two countries."
Nora Lam Gallegos met her future husband at a fiesta in Nuevo Laredo. Arevalo was older, but fun and easygoing.
On Sept. 3, 2012, several months after the cartel massacres, the couple called some family and friends and headed for El Patinadero, a park that hugs a bend in the river.
"We took the girls out of school, and we decided to grill a carne asada," a marinated steak, said Gallegos.
It was still light at 7:38 p.m. when Marine Unit V298 — a 16-foot-long, aluminum boat with an aircraft-sized propeller mounted on the stern — roared up the U.S. side of the river, records show.
Border Patrol Agent Matthew Lambrecht was at the wheel and Agent Christopher W. Boatwright was at his side, according to a wrongful-death lawsuit Gallegos later filed in U.S. federal court in Laredo. Both agents were armed and wore bulletproof vests.
The agents were responding to a report that three people had swum over from Mexico. According to witnesses, one of the three jumped back in the water from the Texas side and was trying to avoid capture by swimming back to Mexico.
The Border Patrol agents gave a different version, saying the swimmer was close to the Mexican shore and needed help.
"The Marine Unit also attempted to assist a subject in distress near the Mexican riverbanks, when they were rocked by approximately 20 subjects on the Mexican riverbanks," they wrote in a six-page, partially redacted Use of Force incident report.
Gonzalez, Arevalo's friend, said in an interview that one agent slung his rifle across his back, and reaching down, tried to haul the swimmer into the vessel with a boat hook.
Edgar Camero, who was grilling chicken, said the swimmer was struggling only because of the boat's wake. He said he shouted, "Leave him! You are going to kill him!"
Veronica Martinez, an American nurse standing near Gonzalez, later saw the same agent peering at the crowd on the shore, raising and lowering his rifle. She pulled out her cellphone and began recording video that shows the airboat near the Texas shoreline.
"They can't shoot at us, because we are on the Mexican side," she told her boyfriend, Hector, according to her statement to Mexican police.
Victor Rojas, a local store owner, said he yelled a warning about families in the park. "Look what you are doing! There are children!"
Gallegos says she told her daughters and husband to get back, to return to the barbecue pit and the birthday celebration underway. Then she heard the shots.
"I saw my husband had blood coming out of his chest," she later told Mexican police, according to their report.
The Border Patrol report says one of the agents — his name is redacted — put his M4 rifle into semiautomatic mode. Then he knelt and fired repeatedly "at a subject on the Mexican riverbanks that was throwing rocks."
Gallegos and three other witnesses interviewed by The Times all denied that Arevalo threw rocks. Nothing in the Use of Force report indicates rocks hit the agents or their boat.
"This thing they said, that there were people throwing rocks, this is a pure lie," said Camero, who was close to Arevalo when he was shot.
The boat's location during the shooting is also in dispute.
Witnesses said it was close to the U.S. shore, too far away to be hit with rocks. The Use of Force report says the vessel was 25 to 50 yards from the Mexican side. The river is about 65 yards wide at that point.
After the shooting, the airboat pulled back to the Texas shore "to seek cover" for several minutes, and then moved upriver, according to the agents' report. The swimmer reached the Mexican shore and climbed out of the water.
Gonzalez crouched in the tall grass until he was sure the patrol boat was gone.
Running over, he saw Arevalo struggling to breathe, blood soaking his yellow shirt. He and Arevalo's brother loaded the wounded man into a white Buick and rushed him to Hospital Especialidades, about 2 1/2 miles away.
Doctors there couldn't find a heartbeat, according to the Mexican coroner's report. They tried to revive him, but he was dead.
The Mexican government condemned the Border Patrol for "disproportionate use of lethal force," and the Mexican Senate demanded action. But the Arevalo case drew little notice in the United States.
Several other cases have become notorious.
In June 2010, an agent shot Sergio Adrian Hernandez Guereca, 15, in the face with a handgun after teenagers threw rocks from the Mexican side of the border bridge to El Paso. "One round struck subject under left eye, subject expired on scene," the Border Patrol Use of Force report states.
Border Patrol investigators decided no charges were warranted. But a federal appeals court in New Orleans allowed the family to sue the agent, saying witness accounts of the shooting "shock the conscience."
And in October 2012, an agent in Nogales, Ariz., shot through a border fence after a rock-throwing incident and killed Jose Antonio Elena Rodriguez, 16. The Use of Force report says the agent fired 15 times. The autopsy says Rodriguez was hit eight times in the back. The FBI is investigating his case.
An independent panel of U.S. police experts reviewed 67 Border Patrol case files at the agency's request in 2012. Their report, kept under wraps for more than a year, was harshly critical of many of the shootings.
Agents sometimes shot out of "frustration," the panel found, or when they could have moved out of potential danger. The report said shootings from boats didn't meet the test of "reasonableness." Records show agents have shot 34 times from boats since 2006.
Border Patrol leaders initially rejected the panel's recommendation to prohibit agents from shooting rock throwers unless their lives were in jeopardy. An internal agency memo obtained by The Times explained that "a prohibition could create a more dangerous environment" by encouraging more rock throwing.
Agency officials say they are making changes.
R. Gil Kerlikowske, who took over as commissioner of Customs and Border Protection in March, says the agency is reexamining 14 shootings. He said he hadn't ruled out disciplinary action in cases under review.
"Right now we are still early into this," he said in an interview.
In March, Border Patrol Chief Michael J. Fisher issued a memo urging agents to move out of harm's way, if possible, rather than shoot. And in May, a Border Patrol handbook said for the first time that agents "shall not" shoot rock throwers unless the agents face death or serious physical injury.
The agency also instructed agents to carry "less lethal" weapons, including pepper spray, Tasers and guns that fire rubber bullets.
Shawn Moran, head of the National Border Patrol Council, which represents about 17,000 agents, said he doesn't believe the new rules "restrict agents from defending themselves" in rock throwings, however.
"Our position is that rocks can kill, and that rocks are deadly weapons," he said.
Arevalo's case still has more questions than answers.
A Border Patrol tower with a surveillance camera stands just upstream and within sight of the rocky beach where he was shot. If the camera was operating, it might establish whether he or anyone else threw rocks, whether the airboat was on the U.S. or Mexican side, and whether the agents were in mortal danger.
Border Patrol officials say they cannot release any video from the tower because of the pending FBI investigation and the lawsuit filed by Arevalo's widow.
The suit claims that the Border Patrol had a "rocking policy" that allowed agents to shoot and kill Mexicans "who allegedly threw rocks at them, regardless of whether [it] posed an imminent risk of death or serious injury to the agents or anyone else, and regardless of whether other, nonlethal means were available to avert any such risk."
Robert Hilliard, a lawyer in Corpus Christi, Texas, who represents Arevalo's widow, said the Border Patrol needed to be held accountable for killing an unarmed man in a crowded park. "Firing an automatic weapon on a group where children are also playing is their first option?" he asked.
Lambrecht and Boatwright, the agents aboard the airboat, declined to be interviewed for this report.
After the shooting, Arevalo's family placed a black cross with his name on the beach where he was shot, but floodwaters carried it away.
Gallegos, his widow, works long shifts in a convenience store to support their two daughters. But they rarely sleep in the cinder-block home her husband built for them.
Local thugs and cartels have tried to shake her down for cash, believing she received compensation from the U.S. government or assistance from Mexican authorities.
She says she has received neither.