Maryland ? As victims of serial arsonist Thomas Sweatt spoke at his sentencing Monday, they said they don’t understand what led him to set random fires that terrorized the Washington area for two years.

“I would love to just find out exactly why he did this,” said Jean Kyler, whose 94-year-old mother still cannot return to her fire-damaged home.

Sweatt, 50, admitted setting 45 arson fires in the Washington area. Investigators know how he did it – using jugs of gasoline and wicks made from clothing. But the reason why went unanswered as a federal judge sentenced him to life in prison plus 136 years Monday.

“To the victims and the victims’ families, I’m very sorry for all the harm I’ve caused you.” Sweatt said.

The former fast food restaurant manager admitted that between February 2003 and December 2004, he set 45 fires in Washington and its Maryland and Virginia suburbs. Under a plea deal, local prosecutors agreed not to charge Sweatt with other arsons.

Sweatt also pleaded guilty to two murder charges. He took responsibility for the June 2003 death of Lou Edna Jones, 86, in her Washington home, and the death of Annie Brown, 91, who died of smoke inhalation a few days after Sweatt set fire to her next door neighbor’s Washington home in February 2002.