A Police officer investigates a double homicide Sunday in the Overbrook section of Philadelphia. Baltimore, Philadelphia and other cities along the East Coast are seeing a surge in killings, say criminal justice experts.

Philadelphia ? Baltimore, Philadelphia and other cities in a bloodstained corridor along the East Coast are seeing a surge in killings, and one of the most provocative explanations offered by criminal-justice experts is this: not enough new immigrants.

The theory holds that waves of hardworking, ambitious immigrants reinvigorate desperately poor black and Hispanic neighborhoods and help keep crime down.

It is a theory that runs counter to the widely held notion that immigrants are a source of crime and disorder.

“New York, Los Angeles, they’re seeing massive immigration – the transformation, really, of their cities from populations around the world,” said Harvard sociologist Robert J. Sampson. “These are people selecting to go into a country to get ahead, so they’re likely to be working hard and stay out of trouble.”

Several possible factors

It is only a partial explanation for the bloodshed over the past few years in a corridor that also includes Newark, N.J., and Boston, but not New York City.

In interviews with The Associated Press, homicide detectives, criminal justice experts and community activists point to a confluence of other possible factors.

Among them: a failure to adopt some of the innovative practices that have reduced violence in bigger cities; the availability of powerful guns; and a shift in emphasis toward preventing terrorism instead of ordinary street crime.

Philadelphia is losing one resident a day to violence, recording 196 homicides through the third week of June. That is slightly ahead of the total at this point in 2006, a year that ended with 406 homicides, the most in almost a decade. On the first day of summer alone, six people were killed in Philadelphia in three street shootings.

Homicides soaring

In Newark, the homicide toll has soared 50 percent in four years, from 68 in 2002 to 106 in 2006. Baltimore had 140 slayings as of June 10, up from 122 the same time last year. Boston had 75 homicides in 2005, a 10-year high, and 75 in 2006. So far this year, there have been at least 30 slayings.

Some cities “never bothered to institute the reforms, policies and programs that impacted violent crime because they felt immune from what they saw as big city issues,” said Jack Levin, director of the Brudnick Center on Violence at Northeastern University in Boston. “Now they’re paying the price.”

These efforts include limiting gun purchases, suing rogue dealers and deploying officers more strategically, based on crime data analysis.

Others blame a resigned acceptance of “quality-of-life” crimes, such as running red lights and vandalism. Some law enforcement authorities argue that ignoring such crimes breeds disrespect and cynicism and leads to more serious offenses.

Most involve guns

The vast majority of U.S. homicides – nearly 90 percent in Newark last year – involve guns. And they are more powerful than ever. The weapons of choice are semiautomatics that can spray dozens of bullets within seconds.

“We’re seeing 40, 45 shots,” said Richard Ross, Philadelphia’s deputy police commissioner. In one recent killing, “I think they fired 20 shots into him. That’s remarkable.” He added: “For some of these young people, it’s the glamour of it. They want to carry on their block.”

The number of police officers per capita has fallen 10 percent since 2000 in cities of more than 225,000, according to Northeastern University criminologist James Alan Fox. Yet post-Sept. 11 fears, especially in Boston, have forced police to monitor government buildings and transportation hubs while also watching for street crime, he said.

Shifted resources

“We’ve shifted our resources from hometown security to homeland security,” Fox said. “We have left relatively unattended the poor and powerless who face violence every day and hear gunshots every night.”

University of Pennsylvania criminologist Lawrence W. Sherman is a prime exponent of the theory that immigration exerts a moderating effect on crime among poor black men.

“Cities that have heavily concentrated and segregated African-American poverty are the places that have increases in homicide,” Sherman said. “The places that have lots of immigration tend not to have nearly as much segregation and isolation” of poor blacks.

Sherman acknowledges the theory is evolving and unproven.

“The fundamental driver of the homicide rate is honor killings among young black men,” Sherman said. “What is it about immigration that tends to tone it down? I don’t think we know the answer to it.”

He said immigrants “change the spirit” of a community and affect the way young black men in poor areas relate to each other.

“It seems a plausible way to account for the big difference in the trajectory of homicides” in stagnant cities versus ones with lots of immigration, he said.

‘I’m not getting it’

The percentage of foreign-born residents is 11 percent in Philadelphia, compared with 22 percent in Chicago, 37 percent in New York and 40 percent in Los Angeles, according to 2005 Census figures.

Alison Sprague, executive director of Victim/Witness Services of South Philadelphia, suggested there is some merit to the theory. Immigrants in Philadelphia tend to be crime victims rather than perpetrators, she said.

“I really do think the vast majority of people are trying to earn a living and support their families and stay under the radar,” Sprague said. Illegal immigrants, especially, “have every motivation not to get involved in something.”

Dorothy Johnson-Speight, of Philadelphia, whose 24-year-old son was shot to death over a parking space in 2001, doesn’t buy it.

“If there were more immigrants in the city of Philadelphia, there would be less violence? I’m not making the connection here. I’m not getting it,” she said.