LAREDO, Texas -- A U.S. Border Patrol agent has been charged with capital murder after telling investigators he killed four female sex workers because he considered them worthless and that he thought he was doing something good for his Texas border city, a prosecutor said Wednesday.

Webb County District Attorney Isidro Alaniz said he will seek the death penalty if Juan David Ortiz is found guilty in the September slayings.

"The scheme in this case, from Ortiz's own words, was to clean up the streets of Laredo by targeting this community of individuals who he perceived to be disposable, that no one would miss and that he did not give value to," Alaniz said at a news conference. Alaniz said the suspect thought he was doing his city a service by killing the women.

Get Breaking News Delivered to Your Inbox

Alaniz has previously said that investigators "consider this to be a serial killer."

Juan David Ortiz Webb County, Texas, Sheriff's Office

Ortiz, 35, was initially charged with four counts of murder, as well as aggravated assault and unlawful restraint. He has been held in Webb County jail on a $2.5 million bond since his Sept. 15 arrest in the border town of Laredo.

Ortiz, a Border Patrol intel supervisor and Navy veteran, seemed to be living a typical suburban life with his wife and two children when the killings occurred. After the first slaying, he continued going to work as usual. He was eventually arrested after he pulled a gun on a woman who was able to escape and asked a state trooper for help.

Authorities have said Ortiz knew most of the victims and that he targeted them for their vulnerability. Melissa Ramirez, 29, was slain on Sept. 3, and 42-year-old Claudine Luera was killed on Sept. 13.

On Sept. 14, he picked up another woman, Erika Pena, who told investigators that Ortiz acted oddly when she brought up Ramirez's slaying and later pointed a gun at her in a gas station, according to court documents. Pena said Ortiz grabbed her shirt as she tried to get out of his truck, but she pulled it off and ran, finding a state trooper who was refueling his vehicle.

Ortiz fled and, he later told investigators, he then picked up and killed his last two victims - 35-year-old Guiselda Alicia Cantu and 28-year-old Janelle Ortiz, a transgender woman whose birth name was Humberto Ortiz.

With Pena's help, authorities were able to track Ortiz to a hotel parking garage where he was arrested.

According to court documents, Ortiz confessed to investigators that he had killed four people. All of the women killed had been shot, but one them died of blunt force trauma, Alaniz said Wednesday.

"The evidence that was presented to the grand jury this morning showed that he killed these four innocent individuals in a cold, callous and calculating way," Alaniz said.