We asked officials, experts and activists what they thought were factors in a decline or upswing in the homicide rate. Here's what they said

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1FRANK ZIMRING, professor at University of California, Berkeley, author of "The Great American Crime Decline":

"The good news about what's happening in Philadelphia is that there isn't any general pattern these days. In St. Louis, homicide rates are up. In San Diego, they're down. Things are good in L.A. and Chicago, not so good in Oakland."

Zimring said the nationwide decline of crime in the 1990s was a cyclical decline that isn't explained by changes in demography, the economy, drug use or imprisonment.

But he said effective police work is keeping crime rates low in New York and Los Angeles, where former New York commissioner William Bratton is running the department.

2POLICE COMMISSIONER SYLVESTER JOHNSON: "When I was deputy commissioner in 1997 we had one of the worst narcotics problems in the country. In 1998 we came up with Operation Sunrise [which flooded high-drug areas with cops] and really attacked the problem.

"In 2002 we came up with Operation Safe Streets and had the lowest homicide rate in years. Since then, I don't know the answer. Crime has gone up nationally, in almost every city. I think there's less federal money from the federal government, not just for policing, but all kinds of programs."

"Most of our homicides now are not drugs or gangs, they're just arguments. We really have to change the mindset of what's going on out there. There are a lot of social problems. Almost 94 percent of those killed are high school dropouts."

3PENN PROFESSOR JOHN DIIULIO, national expert on youth violence:

There are as many theories about homicide rates as criminologists, but "my experiences in New York in the early- to mid-1990s, Boston in the mid- to late-1990s, and Philly in the late 1990s persuade me that what local governments do can make a positive difference."

DiIulio believes a variety of city efforts in the late '90s, including the efforts of then-recreation commissioner Michael DiBerardinis, made a difference in reducing violence.

He is especially supportive of the Youth Violence Reduction Project, an intensive outreach effort to at-risk youths and young adults, and would like to see it expanded citywide.

4JOHN TIMONEY, Philadelphia police commissioner from 1998-2002, now police chief in Miami:

Asked how he got Philadelphia's homicide rate down, he said initiatives such as Operation Sunrise to fight narcotics traffic may have had an impact, along with efforts to get guns off the street.

And his department worked hard on the Compstat process - a series of meetings to discuss crime stats and what commanders are doing to fight crime hot spots.

"It's hard work. It's exhausting," Timoney said. "We weren't abusive or unprofessional, but asked tough questions and tried to hold commanders accountable. I moved a lot of commanders [to different jobs] within my first six months."

5WESLEY SKOGAN, criminologist, Northwestern University:

Skogan said he's looked carefully at Chicago, where crime has been dropping for 16 years. He's convinced changes in poverty or drug use patterns don't explain the trends.

"In the first half of the '90s, it was an increase in incarceration, driven by tougher sentencing laws. In the late '90s and 2000s it was smarter policing - mobilizing communities, going after computer-identified hot spots.

6DOROTHY JOHNSON-SPEIGHT, founder of Philadephia's Mothers in Charge:

Johnson-Speight's son was murdered in 2001, and two years later she founded the group that works to prevent youth violence and support grieving family members.

"I've worked in the schools over the years and interacted with young people, and it seems to me there are more guns available now," Johnson-Speight said. "It just seems younger and younger people are more in tune with where you get illegal handguns."

7RUTGERS SOCIOLOGY PROFESSOR PATRICK CARR, author of "Clean Streets":

Carr says the drop in murders from 1998 through 2002 may be the result of several factors, including demographic changes, and an incarceration binge that followed the drug wars of the 1990s.

He also said the early and mid- '90s homicide rates were exceptionally high due to an unstable street drug trade, and that to some extent the drop is a return to previous levels of killings.

Carr believes the current carnage is the result of the continued widespread availability of guns and the sustained neglect of poor communities by government.

"People feel abandoned," Carr said, "When we ask young people how they ended up in trouble, it's almost a rational response to their lack of options. Too many people have no sense of future and the availability of weapons."

8PENN CRIMINOLOGIST LAWRENCE SHERMAN:

Sherman sees no clear explanation for the decline in homicides several years ago, but favors a strategy of focusing intensively on repeat offenders, with greater efforts at rehabilitation.

9RALPH TAYLOR, professor of criminal justice at Temple University:

"Nobody knows. . . . Like the stock market, there are tons of factors that affect crime on a daily, weekly basis. If you look at the big picture, there was a nationwide crime drop starting in the early mid- or late '90s, and now it's over, though more over in some places than others.

"New York is different in a lot of ways. New York would have lost population in the last census if not for all the immigration, and there are studies going back to the 1930s showing lower crime rates among foreign-born residents.

"In addition [Mayor] Michael Bloomberg has done a lot of innovative things. And Tom Kelly is an incredible police commissioner." *

- Dave Davies