The Mexican government has issued a statement demanding an extensive investigation into Monday’s shooting death of 37-year-old Guillermo Arevalo Pedraza of Nuevo Laredo, allegedly by a U.S. Border Patrol agent.

Issuing its own statement, U.S. Customs and Border Protection said rocks were being thrown from the Mexican side at a Border Patrol boat on the Rio Grande near the International Bridges in Laredo.

“A weapon was discharged by Border Patrol,” said a CBP spokesman. “The shooting is under investigation by the FBI.”

However, a Mexican official said the use of “disproportionate use of force is unacceptable.”

Dora Isabel Lam, Arevalo’s widow, said she and her husband were at a Nuevo Laredo park on the riverbank cooking out, celebrating family birthdays, “because he had not bought us anything.”

She said they and others saw the Border Patrol circling a young man in the Rio Grande who was trying to swim back to Mexico.

“We yelled at them to leave him alone,” Lam said.

She said when the group turned away, they heard gunfire.

“They fired, but I never thought they were shooting at my husband,” Lam said.

She said Arevalo had been standing behind them, so when they looked back they saw him on the ground with a fatal gunshot to the chest.

“My daughter was next to him,” Lam said, as she broke down in tears.

Lam said Border Patrol opened fire toward the Mexican side.

“My husband took the bullet,” she said.