Juan David Ortiz, 35, an intel supervisor for the Border Patrol, was charged with four counts of murder as well as aggravated assault and unlawful restraint, Webb County District Attorney Isidro Alaniz said in a tweet.
Ortiz was arrested after the fifth woman managed to flee. State troopers found Ortiz hiding in a truck in a hotel parking lot in Laredo at around 2 a.m. Saturday. The border city about 145 miles (235 kilometers) southwest of San Antonio.
"We do consider this to be a serial killer," Alaniz said.
Alaniz said that after the suspect picked up the fifth woman she quickly realized that she was in danger.
"When she tried to escape from him at a gas station that's when she ran into a (state) trooper," Alaniz said.
He said that authorities believe Ortiz had killed all four women since Sept. 3. The names of the victims were not immediately released. Alaniz said two of them were U.S. citizens but the nationalities of the other two were not yet known. All of them were working as prostitutes and one was a transgender woman, he said.
"The manner in which they were killed is similar in all the cases from the evidence," said Alaniz.
He declined to discuss the evidence or say how the women were killed.
Alaniz said investigators are still trying to determine a motive for the killings. Authorities said they believe Ortiz acted alone.
"It's interesting that he would be observing and watching as law enforcement was looking for the killer, that he would be reporting to work every day like normal," Alaniz said.
Ortiz was a 10-year veteran of the Border Patrol. U.S. Customs and Border Protection issued a statement saying that it was fully cooperating with the investigation.
"Our sincerest condolences go out to the victims' family and friends. While it is CBP policy to not comment on the details of an ongoing investigation, criminal action by our employees is not, and will not be tolerated," the agency said..
The Texas Department of Public Safety, whose Texas Rangers are investigating, did not return several messages seeking comment.