LAWRENCE – Four of what could easily swell to over 50 witnesses testified Friday as the murder and arson trial of Lynn grandmother Kathleen Hilton got under way in Lawrence Superior Court.Hilton, 62, allegedly torched a triple decker at 44-46 High Rock St. in Lynn on Feb. 24, 1999, inadvertently killing a family of five living on the top floor. She purportedly made threats earlier that she intended to burn down the building where her son’s ex-girlfriend, Krystina Sutherland, lived with Hilton’s two grandchildren, because the woman would not allow visitation privileges.Hilton, who lived nearby at 112 Hollingsworth St., apparently believed if Sutherland was left homeless by the fire, she would be forced to return to her son, Charles Loayza, and perhaps rejoin the family with the children, according to Essex Assistant District Attorney Marcia Slingerland.Defense lawyer Michael Natola rebutted Slingerland’s assertions, contending Hilton is innocent, had no reason to harm her grandchildren, and actually tried to cross a police line at the fire scene in an effort to save them.Natola described Hilton as mildly retarded, with an IQ of 71 and a diagnosed mental disorder. He also pointed an accusatory finger at Loayza, suggesting there are more reasons to suspect him of arson, including an incident just after Christmas 1998 when he allegedly set fire to a holiday ornament attached to Sutherland’s apartment door.Slingerland, the prosecutor, said records show Loayza was at work at Tech Pak in Peabody when the fatal fire broke out. Forrest Lambert, the first witness in the case and a former Tech Pak night supervisor, confirmed as much.The courtroom drama unfolded as Kareem Powell, 26, who as a teenager was visiting his grandmother and aunt on the second floor of the triple decker, told how they escaped the flames. Powell recalled how they ordered takeout food and watched a movie, The Nutty Professor.After the movie, Powell lay on a loveseat to rest from hip surgery and listen to music. He soon spotted flames in the window behind the loveseat, only inches away. Powell’s grandmother, Uscha Powell, now living in Raleigh, N.C., testified she grabbed her pocketbook and a blanket for her daughter’s baby because it was cold outside.”I knew we needed to get out,” she said, explaining how she told her grandson to drop the mop he was brandishing to beat the fire and head for the door. “I saw people jumping out the second floor window.”Kareem Powell did as he was told, hobbling without his crutches and carrying the baby.Uscha Powell said she called out to Herbie, referring to third-floor tenant Heriberto Feliciano, 34, because she could hear coughing coming from the upper floors, She even sent her daughter to warn Feliciano and his family, but the intensity of the fire drove her back.Feliciano and his wife, Sonia Hernandez, 32, their daughters, Sonia, 12, and Maria, 13, and their niece, Glorimar Santiago, all perished.Natola said the prosecution has no physical evidence that indicates the fire was set by an arsonist, other than what resembles the burn pattern made by a flammable liquid. Investigators did not recover any container or other items that might be used to start a fire, nor did a state police dog find any traces, he said, adding that medical personnel who rode with Hilton and her grandchildren to an area hospital did not notice any lingering odor of gasoline or other accelerant during the trip.Initially, police suspected Loayza, who underwent repeated questioning, but eventually turned their attention to Hilton, who has spent the past 10 years at the state prison for women in Framingham.Next door neighbor Kevin Biasetti was the last witness to testify Friday, describing the firefighting effort in the dark and his attempt to keep flames from spreading to his home.The witness list includes firefighters, police detectives, state troopers, arson investigators, a former Daily Item reporter, neighbors, relatives, psychiatrists and co-workers.The