The preliminary cause of the Camp Street fire has been changed from undetermined to suspicious.
The samples submitted to the state fire marshal office in Columbus were ruled inconclusive, said Battalion Chief Paul Ricci.
Inconclusive means "there was not a finding either way that was substantial enough," Ricci explained.
The samples were checked for flammable or combustible liquids that are potential indicators of arson.
The fire department has ruled out electrical and mechanical causes, but arson and human error are still under investigation, Ricci said.
The Sandusky fire department sent in a second set of samples to an independent party. The lab results will be ready next week.
"At this point the investigation is very much ongoing," Ricci said. "We want to make sure we get it right."
On April 3, Brenda Jones watched her house on 625 Camp Street go up in flames.
Firefighters arrived on scene within two minutes, although they searched the home first because of reports that people were inside. No one was home at the time of the fire.
The house was gutted, Fire Chief Mike Meinzer said.
Jones, retired from Delphi, was eating at McDonald's on Perkins Avenue with her 3-year-old granddaughter, Sanai, when she learned of the fire. Her daughter, Chasity Page, called her. Page is Sanai's mother.
Jones lived at the house for 21 years. She and her son are now staying at the Quality Inn.
The damage to the house was estimated at $80,000. Jones has insurance on the house and plans to rebuild on the same lot.
She could not be reached for comment Friday.