LONG BEACH (AP) — Police are pleading for the public’s help finding a gunman who wounded three members of a California family and stole a 3-week-old baby girl who was later found dead in a trash bin near the Mexican border.

Investigators have no leads and no motive for the weekend attack, which took place in a densely populated neighborhood, Long Beach Police Chief Robert Luna said at a Monday afternoon news conference.

“Somebody somewhere saw what happened, and we need you to come forward,” Luna said.

The Los Angeles County Board of Supervisors planned to offer a $10,000 reward for information leading to an arrest and conviction, he said.

The baby, a 10-pound girl named Eliza Delacruz, was found dead Sunday in a trash bin behind a strip mall in Imperial Beach, about 120 miles south of the Long Beach neighborhood where her father, mother and uncle were shot a day earlier.

The mother and uncle remained hospitalized in critical condition.

A homeless man discovered the infant’s body in the city near Mexico, raising the possibility that the assailant crossed or hoped to cross the border. Mourners erected a makeshift memorial of candles and flowers outside a pizza shop at the mall.

“To take a precious child from home, throw her in a dumpster like a piece of trash, is something only a very heartless person would do,” Luna said.

Long Beach detectives believe the family was targeted for some reason but do not yet know the motive, police spokeswoman Marlene Arrona said earlier. They would say only that they are looking for a man who is either black or Hispanic.

The family’s Long Beach residence showed no sign of forced entry, and nothing was taken, homicide Lt. Lloyd Cox told the Long Beach Press-Telegram on Sunday.

“We believe that this is not a random act,” Cox said. “We are going through the backgrounds of all the individuals who live here, but it appears to be very personal.”

The San Diego County medical examiner’s office said it was unknown where or when the infant died before her body was found. An autopsy had not yet been performed, and no cause of death was released.

Aaron Cruz lives next door to the victims’ two-story stucco house in a working-class neighborhood. He said the baby’s father is a veterinary technician who works six days a week and was thrilled to be a dad at age 23.

Cruz, who described himself as the man’s best friend, said the family often hosted large barbecues and parties on their front lawn after moving in a few years ago.

The baby’s parents and uncle lived there with another uncle and the baby’s grandparents, but no one else was there when the shooting happened, Cruz said.

“He had just gotten off work, and this happened to him. It was a normal day for him,” he said. “This was out of nowhere.”

Cruz recalled a large baby shower with dancing that the family threw in November.

“It was his first and only daughter,” Cruz said, as he relit candles that had fizzled out in the breeze. “He was robbed of fatherhood.”

A trickle of mourners went by the family’s home Monday. Christmas lights hung on the porch over a string of yellow police tape, and a wreath decorated the door.

Joseph Guerrero stopped with his wife and 4-year-old son to leave a candle and balloon. He didn’t know the victims but was moved by the infant’s death.

“We have three girls and our son, and when we were picking out the balloon, I just squeezed my daughter’s hand thinking about what they were going through,” he said.

A woman who identified herself as the baby’s grandmother and the mother of the two injured brothers also stopped by but left in tears without going inside the house.

Meanwhile, police defended their decision not to issue an Amber Alert for the baby because they lacked a description of the suspect’s vehicle.

“One of the criteria for that is having a license plate number. We don’t even have that,” Arrona said.

Investigators were asking anyone with information to call or send tips to their anonymous hotline. “We really need the public’s help,” Arrona said.