An investigation is under way after a fire gutted at least one unit at the Hidden Hills apartment complex in University Place Friday morning.

A cell phone picture emailed to KIRO 7 Eyewitness News shows flames pouring out of the unit as crews from University Place and Lakewood arrived at the scene on Morrison Street.

Firefighters cut into the roof of the apartment to vent and douse the flames.

Downstairs neighbor Beverly Olson said she heard three loud explosions inside the apartment before the fire broke out.

"It sounded like someone was breaking stuff inside,” said Olson.

UNCUT: Fire Swallows Apartment

SLIDESHOW: Fierce Blaze Guts Unit

When she and a neighbor walked outside to check out the noises, they saw smoke pouring out from under the door and called 911.

Other neighbors interviewed by firefighters and police also reported hearing the same sounds, University Place Fire Department Deputy Chief Lloyd Christianson confirmed.

Kirk Poindexter, whose brother lives in the apartment, claims the fire was deliberately set by people angry at his brother, who is currently being held in the Pierce County Jail following his arrest several days ago.

"(Firefighters) told me it was set on purpose,” said Poindexter.

The Hidden Hills apartment manager said at least four people were displaced by fire damage.

Management is making other apartments available to them.

Crimestoppers of Tacoma and Pierce County is offering a reward of up to $1,000 for information leading to arrest of the arsonist. Their number is 253-591-5959.