Three people were found dead Tuesday inside a mobile home in Prince William County after an early morning fire, authorities said.

Authorities did not immediately identify the victims but said they all were apparently adults who lived in the home, on Fuller Heights Road in Triangle. Neighbors said a man lived there with his girlfriend and her son, who had recently graduated from high school.

On Tuesday afternoon, family members, who declined to talk to reporters, stood staring at the narrow trailer, blackened by fire and a blue tarp covering the area where the roof had collapsed. The trailer, along with two others, was in a narrow lot near an entrance to Marine Corps Base Quantico.

County fire officials said they were called to the site about 3:20 a.m. by security officers at the base who saw and smelled smoke.

Authorities quickly concluded that two people had perished but were working well into the morning to determine whether a third person had died. Friends of the teenage occupant gathered outside the home, hopeful for good news.

“We were hoping he was all right,” Craig Combs said of the teenager, who often spent the night at a friend’s house.

“Then they put the plastic over everything,” added Darius Bergeron, 19.

By mid-morning, a small crowd of teenagers had gathered, some hugging tightly and sobbing, some silently looking at the sidewalk.

They described a friend who was hard for strangers to get to know but who laughed with his close friends, cheering them up when they were down. They said he played bass guitar and loved rock music. Combs held a bouquet of flowers and said friends were going to have a vigil; they were headed to their usual hangout in the woods.

The fire marshal’s office and police department are investigating what caused the blaze. It will be “a slow, drawn-out process,” said Curt Brodie, battalion chief at Prince William County Fire and Rescue.