A blood feud between groups from the same Dominican town caused the knife attack and shootings that left three men dead last week.

That's the picture that emerged from police who spoke at a forum last night hosted by the JP Neighborhood Council.

Members of the competing Mozart and Boylston gangs attacked each other in a crowded Centre Street pizzeria last Sunday. Winsizky Soto, 27, and Johnnel "Bo" Cruz, 20, of Jamaica Plain and Ariel Dume, 20, of Dorchester mortally wounded each other at Same Old Place restaurant.

The forum drew more than 65 people to the fellowship hall at First Baptist Church.

In addition to the three men killed, a stray bullet injured one woman. Not all wounds are physical, though.

Forty people witnessed the shooting, said Courtney Grey, director of trauma response and recovery at the Boston Public Health Commission. Many of them are suffering from their prolonged, close-range encounter with lethal violence.

High-level Boston Police told forum attendees that while the investigation isn't over, they aren't looking for any further suspects.

"We are not looking for anyone else," said Superintendent Bruce Holloway. "The people who were involved were in the restaurant."

Even so, gang members returned to Same Old Place Sunday night and one of them asked employees what they knew about a man who got away from the shooting, according to a police report. The night of the shootings and stabbing, there was scanner traffic about an SUV seen fleeing from the scene toward Pond Street.

As to the cause of the violence, police pointed to gangs that carry the names of two JP streets.

"It's no secret this was between Mozart and Boylston," Holloway said.

Prompted by an audience member who asked which streets he and his family should avoid, police said it is important not to stigmatize particular streets. Those involved in the feud no longer live there.

"At one point they all lived on these streets," said Detective Lt. Luis Cruz. "Now they've all moved out."

The roots of the conflict go all the way to the Dominican Republic.

"The families are from the same town in the Dominican," said Capt. John Greland of District E-13, which covers most of JP. "Sometimes I think they've forgotten what it's about."

Greland cautioned that the Mozart and Boylston groups aren't large-scale gangs.

"These are not gangs like you see in New York and California," Greland said.

Several speakers said the conflict was complicated, with blurry lines between the two sides.

For instance, Grey noted that he and other trauma workers saw people who attended all three funerals.

"This is a lot more complicated than we think," said State Rep. Jeffrey Sánchez, whose district includes JP and Mission Hill. "These are kids who do have parents looking out for them, but there's something drawing them [to gang activities.]"

As for positive actions JP residents could take, At-Large City Councilor Felix G. Arroyo said people should get to know their neighbors and their neighbors' children, so you know when something is wrong.

 "Own your block," said Arroyo. "In my city I don't want any place to be the wrong place at the wrong time."

Arroyo encouraged neighbors to call 911 whenever they hear or see something suspicious. Police keep track of where 911 calls come from and use it as a factor in deciding how to distribute patrol and other resources.

Police said that for people who want to remain anonymous or not be seen having a patrol car pull up in front of their residence, to call Crimestoppers at 800-494-TIPS or text "TIP" to "CRIME" (27463).

Other speakers said changing routines to participate more meaningfully in JP's vaunted diversity could help.

For instance, Betsy Cowan of Egleston Square Main Street encouraged people to shop in minority-owned stores. In particular she singled out the fresh Guinea hens and other locally sourced food available at Plaza Meat Market.

"If you love diversity, go to Plaza Meat Market," Cowan said.

While the high-profile killings have many JP residents thinking about their safety, crime is down in other categories in the E-13 District. Year-to-date, larcenies from motor vehicles are down 21 pecent (81 fewer incidents); auto thefts are down 15 percent (25 fewer stolen cars); robberies are down 7 percent (11 fewer) and commercial break-ins are down 44 percent. Greland presented these figures at the forum.

Cowan said supporting local businesses could allow more young people to get jobs.

In other JP Neighborhood Council business, council members put off a vote on electing a new member from Area A. That vote is scheduled for Dec. 14.