SAN FRANCISCO (AP) — The case of a Vietnamese ex-con accused of brutally slaying five people in a San Francisco home has shed harsh light on Supreme Court rulings that have allowed the release of thousands of criminal immigrants into U.S. communities because their own countries refused to take them back.

After Binh Thai Luc, 35, spent years behind bars in San Quentin for an armed robbery, an immigration judge ordered him deported six years ago. Instead, he resumed his old life in a quiet San Francisco neighborhood because his native Vietnam never provided the travel documents required for his return.

While Luc's case is a particularly striking one, it is far from uncommon. From 2009 through the spring of last year, records show about 8,740 immigrants were ordered to leave the country after serving time in prison, but Immigration and Customs Enforcement officials let them go because their native countries wouldn't take them back by the time they had to be released from an immigration jail.

Two Supreme Court rulings have established that immigrants who have committed a broad range of criminal offenses can't be locked up in detention indefinitely while they await deportation, and should be released after 180 days unless they are likely to be deported soon. If the government decides they pose a terrorist threat or deem they are especially dangerous, such as sex offenders, some provisions allow for them to be held for a longer period.

ICE put a new immigration hold on Luc this week, and officials said the agency was following the law when they released him after the Vietnamese government ignored their request for his travel documents. The country is one of the slowest in the world to respond to the U.S. government's paperwork requests.

Now, as the investigation into the gruesome San Francisco homicides continues, the political debate over the legal standards that allow criminal immigrants to remain on U.S. soil if their own countries refuse them is flaring again, as it did following a few other high-profile murders at the hands of immigrant ex-felons lingering in the country.

"It is a tragedy that five Americans lost their lives because a dangerous criminal immigrant could not be deported to his home country," said Rep. Lamar Smith, a Texas Republican, who is sponsoring a bill that would challenge the high court's rulings by expanding the pool of immigrants who could be detained for more than six months, perhaps indefinitely, if they can't be repatriated. "Dangerous criminal immigrants need to be detained."

It is "a public safety problem" to release anyone who has committed a violent crime, countered Ahilan Arulanantham, deputy legal director of the American Civil Liberties Union of Southern California. "But the Constitution doesn't give the government to power to lock people up forever, regardless of their citizenship."

Gary Mead, ICE's executive associate director for Enforcement and Removal Operations, testified before Congress in May that he anticipated more than 4,000 immigrant former felons would be released into the community in fiscal year 2011 because their native countries did not cooperate.

ICE statistics provided to Smith's office show 1,012 immigrants with criminal records had been released by April of last year, in addition to 3,882 released in 2010 and 3,847 in 2009. ICE would not provide details about the nature of their criminal offenses, the timing of their previous convictions, or whether they ever were removed. About 4,040 immigrants without criminal records also were released during that time because their home countries would not cooperate.

"Every alien's removal requires not only cooperation within the U.S. government but also the cooperation of another country," Mead testified in May.

Luc's native Vietnam is one of about 20 countries that is slow to cooperate, if it does at all, according to ICE. While Cambodia is least cooperative, the agency said Vietnam was the second-slowest country, taking an average of 218 days to respond to paperwork requests.

International relations also come into play. Citizens of Cuba, which doesn't have diplomatic relations with the U.S., represent about 40 percent of all the criminal immigrants released after serving time, the ICE statistics show. About one of every eight was Vietnamese.

Iran, Laos and Pakistan also "are generally uncooperative," the Department of Homeland Security Office of Inspector General wrote in a recent report.

The high court's rulings make things difficult for ICE officials. Government auditors, however, have raised concerns about whether ICE is doing enough to monitor immigrants who have served prison terms and been released.

In 2007, the inspector general said ICE needed to do more to ensure that dangerous foreign nationals were removed, or that their release was adequately supervised.

In 2008, Cuban national Abel Arango was released after serving time in prison for armed robbery, because the Cuban government would not take him back. He went on to fatally shoot Ft. Myers, Florida police officer Andrew Widman.

Following Luc's arrest Sunday, ICE officials revealed this week that he originally entered the U.S. legally in October 1989 as the child of intending immigrants. But an immigration judge ordered Luc's deportation in 2006, after he served eight years in prison for armed robbery and assault.

Court records show Luc was arrested in two armed robberies of a Chinese restaurant and a clothing wholesaler in San Jose and was convicted in 1996 of second-degree robbery and assault with a firearm.

While holding up the clothing business, Luc said in Chinese with a Hong Kong dialect: "I have a gun, if you move I will kill you," according to the victim's statement to police. He then pistol-whipped the man in the head during a struggle.

After his sentence was up, Luc was shipped to an ICE detention facility in Eloy, Ariz., but was sent back home to San Francisco six months later when the Vietnamese government failed to respond. He was initially required to check in with ICE every month but later was allowed to check in every six months since he was complying with his release requirements. ICE officials said he told the agency he planned to live with relatives and look for work as a cable installer.

San Francisco police still have not revealed the circumstances surrounding the recent slayings, only saying they believe that Luc allegedly targeted the family who lived in the home in the city's Ingleside District.

They have not laid out connections between Luc and the victims, 32-year-old Yuan Ji "Vincent" Lei; his parents Hua Shun Lei, 65, and Wan Yi Xi, 62; his sister Ying Xue Lei, 37; and his girlfriend Chia Huei Chu, 30.

The Vietnamese Embassy did not return multiple messages seeking comment.

Texas Republican Rep. Ted Poe recently filed a bill to block diplomatic visas from being issued to people from countries that deny or delay their citizens' return.

"Why are we issuing visas to anybody from Vietnam until they take back their criminals?" said Mark Krikorian, executive director of the Washington-based Center for Immigration Studies, which advocates for stricter immigration controls.

Still, the ACLU said current congressional proposals would risk creating a scenario where immigrants with a broader range of prior convictions, as well as permanent residents and asylum seekers, could be held indefinitely.

"We live in a world of due process where we don't try to predict in advance, for the most part, which people will commit crimes and lock them up forever," Arulanantham said. "If we did, that would be a frightening world to live in, and would go against our basic notions of liberty."