Federal agents have arrested four people accused of smuggling 131 illegal immigrants found at a "stash house" in south Texas, a U.S. Immigration and Customs Enforcement official said Wednesday. 

The immigrants were also detained Tuesday after a raid at a house near Alton, Texas, about eight miles north of the U.S.-Mexico border, ICE spokeswoman Nina Pruneda said.

The people at the house were from Mexico and Central America, and did not require medical attention, she said. 

The Monitor newspaper, which covers the Rio Grande Valley, said Salvador Hernandez, 52, had just left his house with his elderly parents when the normally quiet neighborhood was suddenly surrounded by ICE agents.

“I have been living here for 28 years and have never seen anything like that happen,” he told the paper.

Border Patrol agents in the Rio Grande Valley, which straddles the southern tip of Texas along the Gulf Coast, have seen the number of so-called "stash houses" used to house illegal immigrants roughly double since October 2011, according to agency figures. 

'Welcome to Hell'
In one of the more brutal recent cases, two men pleaded guilty on Wednesday to harboring 115 immigrants -- some without food or water for days -- in a cluster of stash houses in Edinburg, Texas. 

Vicente Ortiz Soto and Marcial Salas Gardunio, both 23-year-old Mexican citizens, pleaded guilty to conspiracy to harbor aliens on Wednesday in U.S. District Court, according to a statement from U.S. Attorney Kenneth Magidson, who represents the Southern District of Texas. 

Several of the immigrants required medical attention after authorities found dozens of them locked inside a crowded, hot, ramshackle house, according to a criminal complaint filed in the case. 

One immigrant told ICE agents that Salas would greet new arrivals with "Welcome to Hell" when they arrived at the residence and threatened to beat or kill them if they did not remain quiet, court papers state.

Ortiz admitted to driving immigrants to the stash houses from the border and selling them snacks. 

Each man faced up to 10 years in prison and a $250,000 fine at a sentencing hearing set for July. 

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Handout / Reuters

A hand-written memo by then CIA Director Leon Panetta in which U.S. President Barack Obama authorised a Navy SEAL team operation that resulted in the death of Osama bin Laden at his hideout in Pakistan one year ago.

With the first anniversary of Osama bin Laden's death approaching, Leon Panetta has spoken of the nerve-wracking moments of the night of the raid by U.S. Navy SEALs.

The picture in Defense Secretary Leon Panetta's office captures the "mission accomplished" moment. 

It shows Panetta, then the head of the CIA, and a group of U.S. commandos and others in the CIA operations center on the night of May 2 with their arms around each other — a quiet celebration just after U.S. helicopters crossed back over the border into Afghanistan. 

Not until then — 90 minutes after U.S. special operations forces had lifted off from the heavily fortified compound in Pakistan where they went in search of Osama bin Laden — was he sure they could breathe a sigh of relief. 

"We got the job done," Panetta said Friday as he recalled the long silences and the tense, heart-pounding moments before Adm. William McRaven's words finally came through loud and clear. 

"Geronimo EKIA" — the code name for bin Laden, and the signal for "enemy killed in action." 

Abbottabad - One year after Osama bin Laden

With the first anniversary of the al-Qaida leader's death approaching, Panetta spoke to reporters on his plane as he flew back from a series of meetings with defense leaders in South America. Perched on a table inside the Airstream trailer — dubbed the Silver Bullet — that serves as his office inside his C-17 transport plane, Panetta traced back through the nerve-wracking moments of that night. 

And he talked about its impact over the past year. 

"I don't think there's any question that America is safer as a result of the bin Laden operation," he said. 

While al-Qaida and its offshoots remain a threat, he said, the military and intelligence communities have learned to work better together since Sept. 11, 2001. Still, he acknowledged, there is no single, completely effective way to destroy the terror network. 

"The way this works is that the more successful we are at taking down those who represent their spiritual, ideological leadership, the greater our ability to weaken their threat to this country," he said. 

The story of the raid is well-known: The SEALs and special operations forces that flew deep into Pakistan; the wrenching moment when one of the helicopters went down in the heat, landing hard with its tail on the wall; the SEALs' assault on the house where they believed bin Laden and his wives had been living for several years; and what Panetta on Friday called the "fingernail-biting moments." 

"We knew that there were gunshots and firing, but after that we just didn't know," said Panetta, describing the nearly 20 minutes of silence after the SEALs went into the house. 

PhotoBlog: Osama bin Laden's hideout revealed

Then came confusion. McRaven, commander of the operation, told him that he thought he'd picked up the word "Geronimo." 

"The way he said it was like, you know, 'We think,'" said Panetta. "It wasn't ideal. We were still waiting." 

A few minutes later came the KIA message. Then came the long flight out of Pakistan. 

"By that time they had blown the helicopter that was down and we knew we had woken up all of Pakistan to the fact that something had happened," Panetta said with a laugh. "The concern was just exactly what were they thinking and how were they going to respond." 

The moment they crossed the border, he said, was "the moment when we finally knew the mission had been accomplished." 

Then they could embrace the victory. 

The raid created a deep fissure into the already rocky U.S.-Pakistan relations. U.S. officials, including members of Congress, were irate that the al-Qaeda leader had been able to hide — virtually in plain sight — in a Pakistani military town. Some suggested there was at least some knowledge of his hiding place. 

Pakistani leaders, meanwhile, were outraged that the U.S. had launched a military mission deep within the country's borders without alerting them, violating their sovereignty. Islamabad's military commanders were embarrassed that the U.S. was able to carry out the raid without being detected. 

The bin Laden saga has continued in Pakistan. His three wives and their families were deported early Friday to Saudi Arabia. Officials have said that the wives and as many as eight children and some grandchildren were living in the compound when it was raided. 

The anniversary has triggered security warnings for Americans in Pakistan. The U.S. Embassy said its employees would be restricted from restaurants and markets in Islamabad for the next two weeks. While there was no mention of bin Laden, the period includes the anniversary date.

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