SAN JUAN, Puerto Rico — A family of four, including twin boys, was shot to death inside their home in Puerto Rico after celebrating New Year's Eve, authorities said. Police said the couple's 16-year-old son was seriously injured and is hospitalized.

The killings occurred before dawn Wednesday in the northern town of Trujillo Alto, which lies south of the capital of San Juan, according to police. No one has been arrested.

"It's too early to establish a motive," Puerto Rico Police Detective Carlos Nazario told reporters. "We are looking at all angles."

Get Breaking News Delivered to Your Inbox

He said one of those angles could be possible retaliation against an elder son of the couple who is in jail on federal carjacking charges and state weapon and assault charges. Someone allegedly attempted to kill him last week, and when he filed a complaint with police, they arrested him on the pending charges, Nazario said.

He identified the parents as Dorothy Wickline, 47, and Edwin Ramos, 40, and their twins, aged 9.

He said the four of them had celebrated New Year's Eve with relatives and were shot shortly after they returned home.

Police said one person was shot at the entrance of the home, another in the living room and two in the bedroom.