"Everyone anticipated this would be a painstaking and deliberative process," Curry told The Associated Press on Monday.
The explosion caused an estimated $4.4 million in structural damage and scattered debris throughout the neighborhood. Thirty-three badly damaged homes are slated to be demolished.
Experts say explosions and arson cases can take years to close. Nationally, less than 20 percent of 43,412 arsons ended in arrests in 2011, according to the FBI.
Peter Beering, an Indianapolis terrorism consultant and former prosecutor who specialized in arson, told The Indianapolis Star such investigations are difficult.
"First you have to prove what happened. Then comes the whodunit part," he said.
Investigators will have to analyze thousands of pieces of evidence, and even the smallest item can be a vital clue.
"The assumption people make is that an explosion destroys everything," Beering said. "That's far from the case.
"It's all about looking at the smithereens."
Police in 1989 spent more than a year investigating a pipe bomb that exploded in an Indianapolis Kmart store, injuring a 5-year-old girl, before linking it to a knife and screwdriver found in the trunk of a Noblesville teenager's car.