E-Mail This Article to a Friend MASS MURDER Last week’s slaughter — and reaction to it — is nothing new BY DAVID S. BERNSTEIN

Where have we heard this one before? Despite a recent display of police force, including mass arrests in "troubled" neighborhoods, the city was stunned by its worst multiple murder in a decade: someone gunned down several young men in Dorchester, sending Boston’s year-to-date homicide total to its highest since 1995. Church leaders called for action. Police investigated aggressively. City leaders promised action.

That was 15 months ago, on September 4, 2004, when 19-year-old Angelo Henderson, 24-year-old Anthony Williams, and 24-year-old Jason Jenkins were murdered on Floyd Street. A fourth victim, who survived, was found a block away.

The triple homicide brought the 2004 murder tally to 51 — up from a mere 28 by that date the year before. The final toll for the year was 64.

Now it’s happening all over again, following the murder earlier this month of four young men in a basement recording studio on Bourneside Street. The victims this time ranged in age from 19 to 22, and their deaths brought the year-to-date homicide tally to more than 70.

Here’s another similarity between the two incidents: both remain unsolved as of press time. In fact, Boston police have made arrests in just 22 of 87 homicides, beginning with the September 4, 2004, killings through the quadruple homicide on December 13, 2005. That’s a dismal 25 percent, compared with a national average above 60 percent.

The September 2004 massacre and its aftermath offer a poor omen to those hoping that things will change in the wake of last Tuesday’s horrors. Back then, police and city officials bemoaned witnesses’ reluctance to come forward — a reason they are still citing for why they’re not solving the city’s murders. (Some even laid part of the blame on the "Stop Snitchin’" shirts that Mayor Menino would target 14 months later.) District Attorney Dan Conley called for passage of a crime bill that would provide funds for a witness-protection program. He is still begging the legislature to pass it. Likewise, police commissioner Kathleen O’Toole, and several outside observers, pointed to dramatic reduction of the police force as a problem. That shortage still exists, as O’Toole has recently reiterated.

Just like this December’s multiple homicide, the triple murder came after a brutal summer that generated headlines and prompted O’Toole to implement a series of initiatives to stem the violence. It also inspired Reverend William Dickerson, among others, to call on clergy to do more community outreach. Dickerson said much the same at a press conference with Conley this week, where 20 local faith leaders pledged their help. Let’s hope we’re not all going through the same motions in another 15 months.