LAREDO — Texas authorities charged a U.S. Border Patrol supervisor with murder following what they described as the serial killing of four female sex workers and a possible attempt on the life of a fifth woman who escaped at a gas station and found help.

Juan David Ortiz, 35, an intel supervisor for the Border Patrol, was charged with four counts of murder and aggravated assault and unlawful restraint, Webb County District Attorney Isidro Alaniz said in a tweet.

Alaniz described Ortiz as a serial killer.

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 has offered condolences to family and friends of the victims. CBP says in a statement that while it is the agency’s policy not to comment on an ongoing investigation, “criminal activity by our employees is not, and will not be tolerated."

The Laredo Police Department released the following statement regarding the investigation:

The Laredo Police Department is releasing this statement to many concerns over the recent events which involve an ongoing investigation by the Texas Rangers and the Webb County Sheriff's Department. The Laredo PD has also been engaged with the ongoing events and offering our support to the ongoing criminal case. We want to reassure the citizens of Laredo that the community and your families are safe. There has been a recent break through in the investigations and there has been someone detained. That information belongs to the corresponding agencies who are handling the information and will make a more in depth release at the appropriate time. We value the release of timely information and we are making this notice public in order to remove any unnecessary fear in the community. There will be information made available very soon by those agencies who are in charge of the case. Meantime we maintain our city's safety and security and our responsibility to make you feel safe as well. Thank you. - Laredo Police Department