The home owner, identified as Monserrate Shirley, her boyfriend, Mark Leonard, and his brother Bob Leonard, are now facing murder, arson, and other counts.
The deadly blast occurred Nov. 10 in Indianapolis' Richmond Hill subdivision and damaged a total of 80 homes, estimated at a $3.6 million loss.
Shirley's next-door neighboors, identified as John Dion and Jennifer Longworth, were killed in the explosion.
Authorities said Shirley was facing big financial problems, including $63,000 in credit card debt and worsening bankruptcy proceedings. According to Mark Leonard's friend, the couple's woes worsened when Leonard lost $10,000 at a casino weeks before they deliberately set up the explosion.
During the investigation, authorities learned the suspects had removed a gas fireplace valve and a gas line regulator from Shirley's home and then filled up her home with gas. Investigators said they then set a timer on the home's microwave. Once the microwave started, the explosion sparked.
The trio had unsuccessfully tried to blow up Shirley's home the weekend before the explosion took place, according to Marion County Prosecutor Terry Curry.
A day prior to the explosion, the Leonard brothers asked an employee of a local gas utility several questions regarding propane and natural gas.
When a friend of Mark Leonard's called him prior to the blast, Leonard told the friend "the house blew up" and that he and Shirley were staying in an efficiency apartment, according to an affidavit.
In another call, Leonard told his friend he had been surfing Craigslist "looking for a Ferrari to buy." The suspect told his friend he could afford the luxury car because Shirley had jewelry insurance and "they expect to get $300,000 and he would get $100,000" in the insurance payout, according to the affidavit.
It's not clear whether investigators think Leonard believed the first explosion attempt had succeeded.
Shirley and the Leonard brothers face two counts of murder as well as 33 counts of arson - one count for each of the homes damaged so badly that officials have ordered their demolition.
Shirley and Mark Leonard, 43, also face two counts of conspiracy to commit arson, while Bob Leonard, 54, faces a single count. Curry said the conspiracy charges stem from the failed explosion.
Leonard has a criminal record that includes stalking and intimidation and convictions on dealing and possessing cocaine, according to prison records.
Prosecutors said they're reviewing whether to pursue the death penalty or life in prison without parole.
The suspects are scheduled to appear in court Monday.
The Associated Press contributed to this report.
