Police think robbery was the motive in a fatal shooting at a home on Indianapolis' northwest side early Tuesday morning.Police are looking for three men in their late teens or early 20s who were wearing bandanas and carrying handguns as they kicked in the back door of a home in the 3900 block of Kalmar Drive just before 3:30 a.m.Investigators said one gunman went to a room where two teenage boys slept while the other two went to the master bedroom, awakening Mark Fuller, 43, and his girlfriend before demanding money.Police said one of the intruders shot Fuller in the head almost immediately before all three intruders left the home."I heard everything going on. Two guys ran across my back yard," said Randy Pierson, who lives next door. "Come to find out the guy was shot."Fuller underwent a double lung transplant a month ago and had been convalescing at the home of his girlfriend, RTV6's Jack Rinehart reported."Mr. Fuller was done very wrong. It's a shame that people don't care about each other and come inside somebody's home and murder them," said Wayne Harris, Fuller's friend. "Mr. Fuller was a very good guy to me."Police held Northwest District roll call just two houses away from the crime scene in a show of force designed to reassure the neighborhood of officers' mission to protect residents and apprehend criminals."We're going to do our best to try to blanket the area," said Indianapolis police Lt. Homer Hamer.Fuller's girlfriend and the two teens were not injured, and the suspects didn't get any money, police said.Anyone with information about the shooting is asked to call Crime Stoppers at 317-262-TIPS or homicide detectives at 317-327-3475.