Published: Sep 28, 2010 4:41 PM EDT
Updated: Sep 28, 2010 1:42 PM EDT

BOSTON (AP) - A shooting early Tuesday left a toddler and three others dead, and a fifth person was hospitalized and not expected to survive, police said. There have been no arrests, and police have asked for the public's help.

Police responded to the Boston's Mattapan neighborhood just after 1 a.m. Two men and a woman found in the street were pronounced dead at the scene.

The toddler, 2 or 3, died later at the hospital, police department spokeswoman Elaine Driscoll said. A man in his 30s was taken to a hospital and is not expected to survive, she said.

No names were released, and it was too early to speculate on a motive, Driscoll said.

"Right now, it's an extremely active homicide investigation," Driscoll said.

Investigators think the victims knew the shooter, and the commissioner appealed to the public for help in apprehending the suspect or suspects.

Police are looking for a silver or gray Ford Explorer that may be connected to the shooting. The vehicle was seen leaving shortly after the shooting, Driscoll said.

Police recovered a "significant amount of evidence" at the scene, Commissioner Edward Davis said., without getting specific.