A Christmas morning fire that destroyed one Selden business and damaged another is being investigated as an arson -- with surveillance footage showing a man setting the blaze.

Detectives are investigating the fire that started shortly before 4 a.m. Wednesday on Middle Country Road, blowing the doors off a newly opened tanning salon, Suffolk police said Friday.

John Rose and Gene Cella, owners of the 6,000-square-foot strip center that houses Sky Tan, Cella Bagels and Jazz Audio, suspect a competitor. After Sky Tan's opening was announced about six months ago, Cella said he received threatening text messages. Rose said police are "looking into some of these other guys that have a little bit of a beef because now they have a little more competition."

Police declined to comment on the investigation.

Surveillance video from a camera positioned outside the building shows a man approaching at 3:57 a.m. Wednesday, wearing a dark hooded sweatshirt, blue jeans and a backpack. His face is not visible.

He can be seen smashing a hole in one of Sky Tan's glass front doors and going inside. When he climbs back out seconds later, he's carrying a small gas can. He then crouches outside the store and, after several attempts, lights the fire.

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The resulting burst of flames blows off the doors and quickly envelops the salon, the video shows.

Cella Bagel next door was also damaged and will be closed for weeks, the owners said.

Fire crews arrived at the scene within 15 minutes, preventing the fire from spreading through the center.

The bagel shop is open every day of the year except Christmas, Cella said.

On days that it's open, workers show up at 3 a.m. to start baking.

"This act of violence has put 25 people out of work," Rose said. "This is something it took me years to build . . . and these people basically wiped me out in five to 10 minutes."

Cella estimated the damage at about $850,000.No arrests have been made. Police said the investigation is ongoing.