INDIANAPOLIS - Three people have been arrested in the explosion on Indianapolis' south side that killed two neighbors and damaged dozens of homes, as RTV6 first reported Friday morning.

Monserrate Shirley and her boyfriend, Mark Leonard, who lived in the home, along with Leonard's brother, Robert Leonard, were arrested Friday on numerous charges, including murder and arson. John and Jennifer Longworth died in the blast.

Special Section: Indy Explosion

Read: Probable Cause Affidavit

The couple, who lived in the home at 8349 Fieldfare Way along with Shirley's 12-year-old daughter, was visiting a Lawrenceburg casino the night of Nov. 10 when the blast rocked their Richmond Hill subdivision, leveling five homes and damaging dozens more.

All three were charged with two counts of murder, one count of conspiracy to commit arson, 33 counts of arson, a Class B felony and 12 counts of arson, a Class A felony.

The death penalty will be under consideration in the case, sources told RTV6. Damage to homes was estimated at $4 million.

In a news conference late Friday morning, Marion County Prosecutor Terry Curry said the source of the blast was a microwave oven and detailed what is included in the probable cause affidavit.

"The microwave oven … had exploded from inside out," Curry said. "The microwave oven was the point of ignition."

Additionally, a natural gas step-down valve into the home had been removed and a gas valve in the fireplace was missing.

Without the valve, investigators said, it took six to nine hours for the house to fill with gas to reach the combustibility to cause an explosion.

"The flow of gas at that volume would have occurred beginning mid- to late afternoon to reach the volume of the explosion that happened at 11 p.m.," Curry said.

Curry said Bob Leonard and Mark Leonard told investigators that they had last seen each other Tuesday before explosion, but investigators have surveillance video showing they were together Thursday and Friday.

On Friday, prosecutors said, both talked with a Citizens Energy employee, asking that person about gas and the difference between propane and natural gas.

On the day of the explosion, "a resident of Richmond Hill saw a white van … pull into the driveway of the residence between 2 and 3 p.m.," Curry said.

The men were in the home briefly and hurriedly left, investigators determined, and Bob Leonard's son said several items were in the van that had been taken from the home, including photos and financial documents.

Prosecutors said there could be more arrests.

Mayor Greg Ballard issued a statement Friday after the prosecutor's news conference thanking all the agencies who aided in the investigation.

"The announcement of the arrests made today will not erase the scars of that fateful night, but I hope it comforts this grieving community that justice ultimately will prevail," Ballard said.

Prosecutors Detail Failed Explosion Attempt

A probable cause affidavit indicates that steps were taken the weekend before the explosion to create an explosion that weekend.

A cat that lived in the home had been boarded, and Shirley's daughter had been placed with a baby-sitter overnight. Shirley and Mark Leonard went to a casino that weekend, too, Curry said.

Investigators said personal insurance on the home before the blast had been increased to $300,000 and that a thermostat in the house had been changed from a digital unit to a slide switch after the failed attempt. The slide switch creates a spark when activated.

Couple's Financial Troubles

Authorities believe that the the explosion was concocted in a financial scheme.

The Call 6 Investigators have uncovered details pointing to significant financial problems for the couple.

Shirley filed bankruptcy in 2007 with her then husband, but that case was dismissed this June because they failed to make the required payments, documents show.

According to court documents, the home had two mortgages -- one for more than $160,000 and a second for nearly $65,000.

The 9-year-old home with four bedrooms and two and a half baths was put up for a short sale in March 2011, documents show.

The home was initially listed for $188,900, but the price was dropped to $154,900 four months later and to $149,900 in January, before it was taken off the market.

Interview After Explosion

RTV6 interviewed Shirley and Mark Leonard days after the explosion.

"We consider ourselves pretty lucky right now, to be honest with you," he said. "It's miserable, but we're making do with what we've got."

The couple, who spoke in the office of their attorney, said they had lost everything and had endured days of questioning with investigators.

"It's a big devastation, and we're doing everything we can do help the police investigators, the fire department, the (Bureau of Alcohol, Tobacco, Firearms and Explosives)," Leonard said.

"People are talking to me and asking me questions. I mean, I tell everyone the truth," Shirley said. "Everybody's after me, asking me questions.