There are only 14 federal immigration agents for a 5,800-square-mile region of southeastern Pennsylvania and South Jersey with tens of thousands of illegal immigrants.
Agents do not act on police calls unless suspects are criminals or, since 9/11, they are from countries where the government says Islamist radicals operate.
"Before 9/11, if you had a person who was illegal, it was hard to get them picked up," said police Chief Raymond Fluck of Green Lane, Montgomery County. "Now, if it's an Arab or Muslim, they come in a heartbeat. But not for the others."
The result is that police are gambling with their time and resources on suspects immigration agents may not take.
Some police also worry they may be releasing dangerous lawbreakers. And immigrants may face uneven and unfair treatment from town to town.
After 9/11, the Bush administration declared zero tolerance on illegal immigration and urged local authorities to report anyone suspicious as part of its anti-terrorism campaign.
"We're working to take every lead that comes in from those local and state agencies seriously," said Chris Bentley, a Department of Homeland Security spokesman.
But the immigration agency has focused intensively on Muslim nationals since 9/11 - and experts say that sends a message that police must do the same, potentially leading to illegal discrimination.
"It's really the job of the [immigration agency] to engage in that kind of profiling. It's not the job of the state and locals," said Jan C. Ting, a Temple University law professor and former immigration official.
The Bureau of Immigration and Customs Enforcement, successor to the Immigration and Naturalization Service, denies encouraging police to profile but makes no bones about its own selectivity.
The bureau has too few agents, too few judges and too few prison cells to pursue everyone.
"We have to prioritize," said Lance Payne, a Philadelphia bureau spokesman. "If there are no criminal proceedings, even if we find them in the country illegally, we don't respond."
"I am here illegally. You not take me in," said one of the Hispanic immigrants who presented fake state ID cards last May to Patton, the Newtown police sergeant.
Patton called the bureau's Philadelphia office and left a message for Marc Merchiore, its agent in Bucks and Montgomery Counties. Hearing nothing after 40 minutes, Patton jotted down the men's employer, ticketed the driver, and let them go.
"If you're not going to enforce it, then change the law," Patton said.
Merchiore eventually did talk to Patton and endorsed the release, though he denied saying "cut 'em loose."
"With just me doing two counties, and [considering] the workloads of our agents, it's mathematically impossible to arrest and process every undocumented pizza-maker and landscaper," said Merchiore, who did accept Patton's notes on the employer for a potential follow-up.
The priority is foreigners who have warrants or deportation orders, who raise concern about serious crimes, or who come from 33 nations considered "high-risk." Men from two dozen of those countries face deportation if they did not undergo special fingerprinting and questioning.
Most everybody else may be left to police discretion and agent workload. The bureau believes that people it doesn't pursue pose the least danger.
"We cannot predict the behavior of a person once [police] let somebody go," said Associate Special-Agent-in-Charge Bill Riley, the former bureau director for Philadelphia, now in Newark, N.J. "But at the same time, we're looking at past behavior and saying: 'There are people we have to act on immediately.' "
A week before freeing the illegal immigrants, Patton stopped a Mexican driver for having fake inspection stickers. He also turned out to have a handful of fake identification, a long rap sheet, and a ban from entering the United States after being deported.
Patton phoned the bureau's Philadelphia office and alerted its East Coast service center. Six hours later, an agent arrived in Bucks County to stake a claim on the man, Jose Luis Garcia-Torres.
Agent Merchiore calls the case proof that police must learn to call his cell phone directly.
Patton calls it proof of something else: "If I wasn't so tenacious, Philly probably wouldn't have picked him up because they don't have the manpower."
Some local police don't dial the bureau at all.
"With people from Mexico, Guatemala, I just don't call anymore," said Fluck, the Green Lane police chief.
Time and money loom large for small-town departments dealing with an influx of immigrants since the 1990s.
"Our jail is overfilled now," said Chief Mario R. Brunetta of Vineland, Cumberland County, a migrant-worker hub. "If we put an illegal immigrant in jail, they will just get bail anyway."
In cities with large, established immigrant communities, such as Philadelphia and Camden, officers may skip immigration questions as a matter of policy.
"If they are otherwise law-abiding, we will not tell the federal government of their status," Philadelphia Lt. Denny Graeber said. "We were afraid immigrants were not reporting crimes."
New Jersey State Police call if they come across someone with a deportation order or worse, and the bureau usually responds, Sgt. Kevin Rehmann, a spokesman, said. "But if there is no reason to detain them and [the bureau] doesn't want them, we let them go."
For some police, immigrants are a welcome part of the local economy whose legal status is best left to somebody else.
"If there is a [traffic] violation and they're stopped, they're issued a summons and that's it," said police Chief Frank Ingemi of Hammonton, Atlantic County, home to many blueberry farms. "Immigrants . . . do serve a purpose here by picking crops. They're willing to do that, and they're hired and they're good workers."
Complaints turn to compliments when police discuss the federal response to calls about Muslim or Arab immigrants.
On March 18 in Marcus Hook, Delaware County, police pulled over two Arab-looking men driving slowly near an oil refinery.
Federal agents quickly detained them. One was a Yemeni-born U.S. citizen who was released. The driver - a Jordanian charged with violating his student visa by holding a gas-station job in nearby Chester - was jailed by immigration. Now free, he faces deportation.
Last April, federal agents jumped when police in Mount Laurel, Burlington County, called in a citizen tip about a gas-station worker who allegedly resembled a wanted terrorist.
"He was legal," Lt. Robert Marter said. The worker was released in half an hour. "Before [9/11] it wouldn't have happened like that."
Nobody faults the focus on potential terrorists. But the notion that agents may be tacitly encouraging profiling by police inflames debate.
"They are telling them to profile, and it's not so subtle," said Angela Kelly, deputy director of the National Immigration Forum, an advocacy group.
The bureau defends its priorities, saying agents are obligated to scrutinize people from high-risk countries. But it denies encouraging police to single out people by ethnicity in traffic stops or other routine work.
"We don't encourage racial or nationality profiling," said John Torres, special-agent-in-charge for New Jersey. "We won't stand for that."
The immigration agency, conceding its enforcement failures, is making changes since 9/11:
Police may call bureau agents' cell phones directly.
The bureau is installing video-teleconferencing equipment in more local courthouses, enabling an agent to attend hearings electronically.
The bureau's service center now makes files accessible to police by phone or e-mail at any time.
The bureau has put records of certain criminal aliens and deportees into the FBI's National Crime Information Center database, a favored police tool.
More immigrant files also are part of a digital fingerprint scanner available to some larger police departments.
In June, the scanner helped Bensalem police identify a drug trafficker who had given a false name during a traffic stop. The Trinidadian man, found with 10 pounds of marijuana, had been deported six months earlier.
With swift cooperation from Merchiore, police had him jailed, Bensalem Officer David Clee Jr. said.
But in a case two weeks before 9/11, Clee's inability to reach an agent overnight allowed a once-deported felon to slip back into the community, he said.
"I think it's moving in the right direction," Clee said. "It's just not there yet."
Recent advances might have helped in April 2001, when police in Florida stopped an Egyptian student who was driving without a license. His immigration status was in limbo. But he wasn't listed in the FBI database, so police let him go with a ticket.
He was Mohammed Atta, one of the 9/11 hijackers.
A more ambitious, and controversial, solution would be giving local police the authority and training to investigate and handle some immigration cases, something that is already happening in Florida and Alabama. A bill in Congress would offer training to all police departments.
Currently, the region's 14,500 state and local officers can enforce only state or local crime statutes. That means police can book a foreigner on a local offense, such as using a fake ID. But they must hand off to federal authorities for the immigration charge, such as having no visa.
Immigration critics want police fully engaged to help snare the nation's estimated 7 million to 10 million illegal immigrants.
"Their involvement in immigration enforcement would be a tremendous force multiplier," said James Edwards, researcher for the Center for Immigration Studies in Washington.
But immigrant advocates say police may end up discriminating against and scaring immigrants from reporting crimes.
Police themselves are split.
"They put so much burden now on law enforcement with this whole 9/11 thing," said Frederick Harran, Bensalem's deputy director of public safety. "And they've given us no resources."
Contact staff writer Thomas Ginsberg at 215-854-4177 or firstname.lastname@example.org.
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