New York State Police are once again asking for the public's help solving a heinous 1986 double homicide -- a case where a man allegedly shot his own son 18 times and stabbed the son's friend twice, killing both of them. 

William Fischer has been on the run since the Long Island killings of his son, 19-year-old Billy Fischer, and Billy Fischer's friend, Nancy Hyer. Their bodies were found in the trunk of Hyer's car four days before Christmas in 1986. 

State Police say Fischer apparently invited his son to his Southampton home on Dec. 10, 11 days before the bodies were found. During the visit, authorities believe Billy Fischer, who suffered from cystic fibrosis, asked his father for money to help cover his mounting medical bills. 

The next day, Billy Fischer contacted Hyer and asked her to come get him from his father's house. When she arrived, William Fischer allegedly shot his son over and over again, then stabbed Hyer to death, putting their bodies in Hyer's trunk and dumping the car at the Southampton Elks Club, State Police say. 

Cops searching William Fischer's home found blood and fibers matching the victims in the vacuum cleaner; they also found bullets in the walls. Luminol sprayed throughout the house revealed blood had been cleaned off the walls as well, investigators say. 

William Fischer was indicted on two counts of second-degree murder months later, on Feb. 25, 1987. Two days later, his car was found abandoned at John F. Kennedy International Airport. Authorities have not been able to find him. 

William Fischer is now 72 years old. He's described as being about 5 feet 11 inches tall and 185 to 200 pounds with salt and pepper hair and blue eyes. Anyone with information on his whereabouts is asked to call State Police at 631-756-3300.