PHILADELPHIA (WPVI) -- Family members hope a billboard campaign will lead to answers in a man's 2008 unsolved murder.Two billboards are posted in New Jersey, one in Camden and the other in Pennsauken.In September 2008, 24-year-old Matthew Novak Jr. was in Philadelphia for the annual Puerto Rican Day Parade, when his friend's car broke down at 6th and Green streets in Northern Liberties.Three men stopped to help, offering to take Novak to get some jumper cables, police said.Minutes later, police said the men drove Matthew to the area of 13th and Fairmount, and shot him as he was trying to get out of the car. He died later at the hospital.Police said the persons of interest were seen driving a 2006-2008 blue Chevy Impala with New Jersey tags.Novak's family is offering a $42,000 reward for information that leads to an arrest and conviction in this case.