Marion County Prosecutor Terry Curry said search warrants are being executed and interviews are being conducted, though he declined to say who had been interviewed or what investigators have found. He and other authorities announced Monday that the case was now being treated as a criminal homicide investigation.
"As we learn information and learn the identities of individuals who might or might not have information, we're pursuing every lead along that line," Curry said Wednesday.
Indianapolis' code enforcement department said Wednesday that it had issued demolition orders for 29 heavily damaged homes in Richmond Hill, a subdivision on Indianapolis' south side. Four other homes, including two that were leveled in the blast, are being maintained for now as part of the crime scene.
Owners of 17 of the 29 homes under demolition orders have until Dec. 20 to consult with an engineer to determine if their home can be saved, said Adam Collins, deputy director of the city's code enforcement department. But he added that some of the subdivision's homes are so badly damaged they are in danger of eventual collapse.
"With all of these homes we believe they should come down because they pose a safety risk," he said. "We believe they're not repairable."
The four houses at the crime scene include the home where investigators believe the explosion occurred and the house next door, where the couple killed in the blast — John and Jennifer Longworth — had lived.
The owners of the house believed to be the blast site weren't home at the time of the explosion.
City arson investigators, along with agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives, have concluded that the late-night blast was not an accident. Total damage has been estimated at $4.4 million, and federal authorities are offering a $10,000 reward for information in the case.
Investigators have focused on appliances in their search for a cause.
Curry said investigators are continuing to "narrow down the precise mechanics of the explosion." But the prosecutor said he could not comment on what investigators believe may have lead up to or triggered the blast.
"The belief at this time is that it was an intentional act, but other than that, I can't discuss how investigators might or might not think that occurred," Curry said.
Monserrate Shirley and her boyfriend, Mark Leonard, lived in the home where authorities believe the blast occurred — but the couple was at a southern Indiana casino at the time of the blast. Shirley's 12-year-old daughter was staying with a friend, and the family's cat was being boarded, said their attorney Randall Cable.
Cable said Shirley's daughter had told her mother she had smelled an odd odor in the home in the weeks before the explosion, but they had not reported it. Shirley has said that her boyfriend had replaced the home's thermostat and their gas furnace was working.
Cable said Wednesday that the couple has been cooperating with authorities in the probe but is weary of being pursued by reporters asking questions about the explosion.
"They're just tired of being hounded," he said. "They continue to say that they're victims, just like everybody else."