(CNN) — When San Antonio Police officers responded to the scene of a tractor-trailer with dozens of migrants inside, they were hoping to rescue the occupants, Police Chief William McManus told CNN. Instead, they discovered a scene “beyond tragic.”

“This was a crime against humanity. This was nothing but pure evil, that someone could allow this to happen, to anyone, let alone that many people,” the chief said.

McManus, who has been in law enforcement since 1975, was reluctant to describe the graphic scene.

“The floor of the trailer, it was completely covered in bodies. Completely covered in bodies,” he said. “There were at least 10-plus bodies outside the trailer, because when we arrived, when EMS arrived, we were trying to find people who were still alive. So we had to move bodies out of the trailer onto the ground.”

In emergency responder radio traffic posted on the scanner website Broadcastify.com, one person can be heard requesting more help at the scene. “I have too many bodies here,” the man says.

About 10 minutes later, another man says: “We’re going to need someone to process. Everyone on scene, including my DI’s, are tied up with assisting. Got approximately 20-plus victims.”

No further victims were found after a search of the area with K-9s, McManus said.

In all, 53 people died in what one Homeland Security Investigations’ agent called the deadliest human smuggling incident in U.S. history. Some victims could be younger than 18.

When San Antonio Police officers responded to the scene of a tractor-trailer with dozens of migrants inside, the floor of the trailer was covered in bodies, police chief says. (Nicole Chavez/CNN)

Authorities in Mexico, Guatemala and Honduras have said they are collaborating with the U.S. in trying to identify the people who died.

The suspected driver of the truck was spotted attempting to leave the scene, McManus said. In the recording on Broadcastify, one person says the man was seen running near some railroad tracks while another says to keep a lookout for the driver, thought to be a man in a brown shirt.

The chief said a police helicopter followed the suspect, who was ultimately detained in a field. The chief did not go into the condition nor demeanor of the suspected driver.

Homero Zamorano Jr., 45, was arrested Wednesday, according to a news release from the U.S. Department of Justice. Surveillance footage from a camera at an immigration checkpoint showed the driver of the 18-wheeler wearing black stripes and a hat.

“(San Antonio Police) officers were led to the location of an individual, later identified as Zamorano, who was observed hiding in the brush after attempting to abscond. Zamorano was detained by SAPD officers,” the DOJ release said.

Zamorano, who lives in Pasadena, Texas, is accused of one count of alien smuggling resulting in death, according to the release.

CNN has been unable to determine whether he has an attorney.

The U.S. Attorney’s Office in San Antonio has filed a motion requesting Zamorano to be detained without bond, citing “a serious risk that the Defendant will flee,” court documents show.

The motion also noted that Zamorano’s felony offense, transportation of undocumented immigrants resulting in death, “involves a minor victim.”

According to Zamorano’s criminal complaint, he was escorted to a local hospital for medical evaluation after San Antonio police officers encountered and detained him at the scene. A cell phone, hat, and wallet containing Zamorano’s ID card were recovered from his person and the immediate area, the complaint added.

Three other individuals have also been arrested and charged in connection with the case.

Eleven still in hospitals

Eleven of the 16 survivors are still hospitalized, according to U.S. Immigration and Customs Enforcement. At least two patients are in critical condition, hospital officials said.

Gustavo García-Siller, the archbishop of the diocese of San Antonio, said most of the survivors were unresponsive or could not communicate due to their conditions when he visited them earlier this week.

“They were all hooked to machines and some intubated, so there was not a possibility of dialogue. My place was to pray, to think about their families. I spoke to some of them without receiving any reaction back but I knew that I was speaking to real persons in suffering and that God knows their hearts,” García-Siller told CNN.

After visiting the six hospitals where the survivors have been treated, the archbishop said he could only speak with a 16-year-old girl from Guatemala. The girl had not been able to reach her family because she had to give up her phone, García-Siller said.

“The dialogue was to assure her that everyone there was there to help her, that she was alive,” he said.

“She was the last one that I saw, seeing all the rest, she seemed to be in very good shape and the nurse told me she was fine but they needed to keep her to be sure. In her reactions, she was not very talkative, surely as expected,” he added.

The archbishop said at another hospital he was able to communicate with another survivor only through hand gestures.

“I invited her to trust, I assured her that she has made it and that we hope that she would make a full recovery. For immigrants (it) is very difficult to trust people around them, especially if you see one, two officials at the door of your room,” he said.

García-Siller said he has worked with migrants since the 1980s but has never seen such a large group of people die in a single incident.

“People were abandoned to die. They were dying, burning inside of that place, you can imagine with no water, no food, with natural physical needs. It’s hard to picture what happened in that box, dark box. I invite you, respect people. People are people. Treat others as you would like them to treat you,” he said.

A memorial to the victims

A makeshift memorial continues to grow at the desolate road in the outskirts of San Antonio where the truck was discovered.

Mostly in silence Wednesday, dozens of families placed flowers, candles bearing images of the Virgen de Guadalupe and gallons of water — a nod to how migrants carry water on their trek to the U.S.

Just a few feet away from an Honduran flag, the word “migrants” is crossed out on a sign that now instead reads as “53 humans!”

Among those visiting the memorial, some people wore the Honduran national soccer team jersey, and many spoke Spanish and Indigenous Mayan languages as they prayed or held their phones up, showing the memorial during video calls with relatives outside the US.

“My aunt in Honduras asked me to call her from here, she is the one who first told me about what happened,” a woman who had been on a video call said.

A second memorial surrounding pieces of clothing and two pairs of black sneakers began Wednesday several yards down the road. A group of people believing the clothing may have belonged to some of the migrants in the truck, laid them flat and placed a pair of candles around them.

Texas to increase truck checkpoints

On Monday, the truck went through a checkpoint north of Laredo, Texas, according to U.S. Rep. Henry Cuellar, a Democrat whose sprawling district includes Laredo and San Antonio. It was discovered nearly 150 miles north of the border.

Texas Republican Gov. Greg Abbott announced Wednesday the state would add truck checkpoints and the Department of Public Safety (DPS) “will create and implement a checkpoint strategy beginning immediately where they will begin targeting trucks like the one that was used” in this incident.

Abbott also said the state is creating two strike teams to “detect, deter and apprehend” unlawful crossings of immigrants.

The teams, which comprise 20 troopers each, will be deployed in the border town of Eagle Pass, according to Abbott, and additional units will be deployed to “high traffic crossing areas as needed.” The governor said the resources were being deployed to “mitigate President Biden’s growing border crisis.”

The Biden administration earlier this month launched what U.S. Homeland Security Secretary Alejandro Mayorkas called an “unprecedented” operation to disrupt human smuggling networks amid soaring numbers of migrants at the southern border.

After Monday’s horrific discovery, Mayorkas said on social media: “Far too many lives have been lost as individuals — including families, women, and children — take this dangerous journey.”

White House press secretary Karine Jean-Pierre repeated those words at a briefing Wednesday. “As Secretary Mayorkas said, far too many lives have been lost to this dangerous journey. We will continue to take action to disrupt human smuggling networks, which have no regard for lives. They explode — exploit and endanger in order to make a profit,” Jean-Pierre said.

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