Rosas was believed to be carrying a black Heckler Koch (HK) P2000 .40 caliber service pistol at the time of his death.
The FBI offered a big reward Wednesday for a gun taken from a Border Patrol agent who was shot to death last week near Mexico.
Robert Rosas's body was found on Thursday night near Campo. The 30-year-old agent was killed while responding alone to a suspected border incursion near Campo. He was shot in the head and body, said Keith Slotter, special agent in charge of the FBI's San Diego bureau.
On Tuesday, the FBI said anyone with information leading to the recovery of Rosas' missing black Heckler Koch (HK) P2000 .40 caliber service pistol would be eligible for a $10,000 reward. There is a separate $100,000 reward being offered for information leading to the arrest and conviction of the individual(s) responsible for Rosas' slaying.
"We believe that his weapon was taken at the time of his killing, and this is considered a key piece of evidence in this case," said FBI special agent Darrell Foxworth.
Over the weekend, Mexican authorities named a man accused of murdering Rosas. The country's federal police said the alleged gunman is Ernesto Parra Valenzuela, 36. He was arrested Friday in Tecate. At the time, it was reported that Valenzuela was carrying a Border Patrol-issued pistol, but the FBI said Wednesday that they are looking for a different weapon than one shown in a photograph taken after Valenzuela's arrest.
Mexican police also announced the arrests of four men Saturday near Tecate who are suspected of involvement in the fatal shooting. Federal investigators also arrested three people at a San Jose, Calif., hospital, but it's not known what role they may have played in the killing.
Mexico police did not say what evidence they had against the four, whom they identified as Jose Quintero Ruiz, 43, and his brother Jose Eugenio Quintero Ruiz, 49; and taxi drivers Jose Alfredo Camacho, 34, and Antonio Valladares, 57.
Anybody with information concerning this case is being urged to contact the FBI at 858-565-1255. Tipsters can remain anonymous, according to the FBI.
Rosas, a three-year Border Patrol veteran, had a 2-year-old son and an 11-month-old daughter.