HOUSTON -

Fire investigators spent Monday carefully inspecting every charred piece of evidence at the scene of Friday’s deadly hotel fire.

Officials are looking for clues into what caused the fire which killed four Houston firefighters.

“It could take a month to recreate where everybody was, what they were doing and what caused the tragedy,” said Capt. Ruy Lozano at a Monday afternoon press conference.

Lozano said the State Fire Marshal’s Office is leading the investigation. Authorities with ATF and the Houston police homicide unit are assisting with the investigation.

“We have no evidence or information that this was a set fire or that anything happened that shouldn’t have happened, expect that four firefighters died and another is in critical condition,” said Mayor Annise Parker.

Investigators said the first 911 call to report the fire was made at 10:27 a.m. Friday. At 12:11 p.m., the first units were on scene and within minutes, a distress call was made concerning the safety of the firefighters.

More than 200 firefighters were involved in fighting Friday’s fire. They have been offered counseling to cope with the loss of colleagues and to help them return to duty at fire stations that are now overshadowed with sadness.

The public is invited to attend a memorial service for the four fallen firefighters. It will be held Wednesday at 10 a.m. at Reliant Stadium.