Prosecutors contended that the trio filled the house with natural gas and then used the spark from a microwave which could be set in advance to detonate it. The alleged motive for the arson was to collect insurance money to ease financial strain. Shirley would receive over $300,000 in insurance money for the replacement of the home as well as personal items. Investigators found that the couple had substantial debt, including $63,000 in credit card debt, and were in bankruptcy proceedings. A friend of the couple reported that Mark Leonard had lost $10,000 at the casino approximately three weeks before the explosion. A second mortgage had been taken out on the home for $65,000 in addition to the original mortgage of $116,000.
