A living facility being built for HIV/AIDS patients was the target of a small arson fire this morning in the Walnut Park neighborhood of St. Louis.

Three different sections of the site were set on fire, but only one was still flaming when a construction crew arrived at about 6:30 a.m and was quickly put out by the workers.

The fire was set hours before a news conference to discuss the project, an 18-unit residence for HIV/AIDS patients who are homeless or at risk of being homeless.

The press conference went on as planned, featuring Mayor Francis Slay and Alderman Greg Carter. The building, in the 5800 Block of Harney Avenue, is set to be finished later this year.

The fire comes as police are investigating three cases of possibly-connected arsons at residential construction projects on South Grand and Lafayette Square.

But there is no indication today’s fire is linked — police said it appeared to be the work of vandals.

Though it does bear some similarity to the earlier fires– all were started early in the morning at construction sites – the previous incidents were at pricey condo developments that suffered far more destruction.

Today’s fire was at subsidized housing sponsored by Doorways, a local organization that provides housing for individuals with HIV/AIDS.

Matt Teter, a spokesman for Doorways, confirmed that police believe the fire was an arson, but the motivation remains a mystery.

"We have no idea at this point," he said.