Just hours after law enforcement made an unusual appeal to a bomber in Austin, Texas, there was another explosion, wounding two men.  Austin police say this fourth incident “clearly is the work of a serial bomber.”

Earlier Sunday at a news conference, police reached out to the person responsible for the random attacks. From The New York Times:

“These events in Austin have garnered worldwide attention, and we assure you that we are listening,” Chief (Brian) Manley said in addressing the unknown bomber or bombers at the earlier news conference. “We want to understand what brought you to this point, and we want to listen to you.”

The latest incident occurred Sunday night in the southwestern part of the city, and according to the police chief, showed a different level of bomb-making sophistication.

Austin police are asking residents in the area of this latest bombing to remain indoors until later today and to turn over any security camera footage that might show who placed the bomb.