"Laredo's not the sleepy town that we all grew up in", Alaniz said.
Juan Davis Ortiz, 35, a former US Navy vet, who has been with the US Border Patrol for 10 years was captured by the state troopers on Saturday in Laredo, a Texas city on the border with Mexico.
According to his booking records he is being held on $2.5million bond.
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"We have very strong evidence that he is the person who has been killing", Webb County Sheriff Martin Cuellar said at a news conference posted on KGNS's Facebook page.
Two of the victims were found earlier on Saturday and on Friday evening.
Law enforcement officers gather near the scene where the body of a woman was found today near Interstate 35 north of Laredo, Texas.
The woman who escaped said Ortiz picked her up in a white pickup truck and took her to his home, according to an affidavit. The 35-year-old reportedly carried out his crimes from September 3 to September 15.
The victims were shot in the head.
Authorities said that nearly had no doubt that Ortiz was behind the gruesome acts, with Webb County Sheriff Martin Cuelllar stating that police are in possession of "very strong evidence" implicating Ortiz. She told police she struggled with Ortiz but was able to flee. A motive for the killing was not given. The mother of two was found on a road in rural northwest Webb County, the AP says. Ortiz told investigators that he picked up an unknown woman whom the document identifies only as "Jane Doe".
Alaniz is also overseeing another case involving a Border Patrol agent in Laredo, a man accused of killing his lover and their 1-year-old son.
"When she tried to escape from him at a gas station that's when she ran into a (state) trooper", he said. Luera was found still alive but in critical condition Thursday near a stretch of Texas Highway 255, but she died at a hospital. But Ortiz does not appear to have known the last two victims, he said.
"David grabbed her shirt to prevent her from exiting the vehicle". She managed to jump out of the truck and into the night, her shirt torn from her body.
According to the affidavit, after Pena escaped Ortiz's vehicle at the gas station, he went on to kill two more people that same evening.
At least two were US citizens; the nationalities of the others were not known and investigators are still working to determine a motive.