Returning home yesterday morning after a quick trip to the store, a 33-year-old woman pregnant with her fourth child was shot in the leg on a busy stretch of Hancock Street in Dorchester, leaving police baffled about the motive.

The victim, identified by relatives as Maria DePina , was rushed to Boston Medical Center. "She was surprised, shocked. She's talking pretty well now, worried about the baby first, but they told her the baby was OK," her niece, Dirma Lobo , said moments after returning from her aunt's bedside.

Boston police spokesman James Kenneally said the motive for the shooting is unclear.

Police initially suspected that DePina was targeted, but later were told by DePina through an interpreter who speaks Cape Verdean Creole that she did not know the shooter.

"She couldn't describe anyone," Kenneally said.

A tan van was seen leaving the area. Police recovered ballistics evidence from the scene but have not disclosed what type of handgun was used.

The shooting occurred while a press conference was underway nearby at the Dorchester House Multi-Service Center with law enforcement officials, city councilors, and community activists on hand to announce "Boston's Peace Month." Police Commissioner Edward F. Davis , who was at the event, quickly arrived at the shooting scene.

"It was an absolute coincidence, but that's an example of why we have to figure out a way to end the violence," s tate Representative Byron Rushing , who also attended the antiviolence event, said in a telephone interview.

While the number of homicides is up in Boston so far this year compared with last, the number of shootings was down by 22 percent through Sunday.

Lobo said DePina was returning home at about 10:30 to get ready for her job at the Hub Folding Box Co. in Mansfield when she was shot in the right leg at the corner of Hancock and Dewolf streets . "She was just walking, minding her own business, then she looked down, felt her leg hurting," Lobo said.

"This area is quiet, she never talked about having any trouble," Lobo said. "She's confused."

Lobo said DePina, who is seven months' pregnant, is married and has three children, ages 9, 7, and 5. DePina's brother lives with the family in a third-floor apartment in Dorchester.

A coworker who regularly gives DePina a ride said she is quiet and hardworking.

"I dropped her off last night, like I always do, and she was fine," said the coworker, Joao Pereira.

"I don't know why anyone would want to shoot her."

Brian R. Ballou can be reached at bballou@globe.com.