The blast on November 10 destroyed more than 80 homes and killed two residents. Late Monday afternoon, authorities announced that the explosion was "criminal homicide" and not an accident as first thought.
Police are now looking for a possible getaway vehicle from the blast scene and there is a reward for information leading to suspects.
It is Indianapolis's Homeland Security chief who says that this was the result of a criminal act. Investigators would not take questions at its Monday briefing, so there are no details what authorities suspect motivated the bomber or bombers, nor how the blast occurred.
This surprising development comes a little more than a week after the explosion that damaged 81 of 125 homes in the subdivision and completely flattened five others.
Dion and Jennifer Longworth died in the explosion. The couple, in their mid-30s, lived in a home adjacent to the epicenter of the explosion.
Their funeral was Monday.
Federal agencies and a local Crime Stoppers group have posted $11,000 in rewards. Police say they are especially interested in information about a white van that was seen in the area right at the time of the explosion.
Police impounded a white van right after the explosion, but it isn't clear whether that is the van they are still interested in.
Monday's developments are the result of information from both search warrants and interviews with witnesses.