Local and state investigators are looking into a rash of deliberately set house fires in Lafayette, with seven vacant structures burning within a week, including one set ablaze Tuesday morning.

All the fires except the first occurred early in the morning, and all were set while it was dark. No one so far has been hurt or killed, officials said.

“Since last week we’ve been working diligently to develop leads and suspects,” Lafayette Fire Department spokesman Alton Trahan said.

Answers remain elusive: Is it the work of a serial arsonist? A gang of kids seeking thrills? Are the latest fires the work of copycats? Are the fires being set by homeless people who sometimes seek shelter in vacant dwellings?

“Out of the seven, so far, we know of at least three had transients living in them,” Trahan said. “But we cannot make any determination of their involvement in any of the fires.”

Lafayette police and fire investigators, along with arson detectives with the state Fire Marshal’s Office, have gone into each dwelling to locate where the fire started and look for evidence of how it started.

Trahan said K-9 teams with the Fire Marshal’s Office have sniffed through the debris to determine if accelerants were used and, if so, what they were. Despite the hours spent examining the evidence, authorities have not succeeded in determining what was used to start and spread the flames.

So far, no dwellings surrounding the burning structures have been damaged, but that may be the result of good luck.

The latest fire, on Armentor Street early Tuesday, consumed a wooden structure that has an active gas line and meter behind it. The dwelling’s owner, Ronald Armentor, said the gas line feeds the 20 or so mobile homes in Armentor Park, including two within 20 feet of the home and the gas line.

“I keep a pretty tight watch on the place,” Armentor said. But neither he nor any of the park residents noticed anything or anybody strange lurking lately, he said.

Armentor said one of the park’s tenants called him early Tuesday to tell him the news. Armentor said he later learned it was employees at a nearby McDonald’s restaurant who saw the flames and called the Lafayette Fire Department.

Lafayette Fire Chief Robert Benoit said he’s telling residents to be vigilant and to look especially for strangers roaming the neighborhood who do not seem to belong.

“Call us or police if you see anything unusual; watch your surroundings,” Benoit said.

Trahan said the first fire — at 9:37 p.m. June 11 — was the only one not started between midnight and dawn. Some were started inside the houses, while others were started on the outside, he said.

The activity has taxed the department and its firefighters.

Trahan said 20 firefighters and three to four firetrucks responded to each blaze. The June 12 fires on Dolese and South Magnolia streets burned within 94 minutes of each other and required a response by most of the firefighters Lafayette had on duty that morning, Trahan said.