WATER MILL - The search is on for a hit-and-run driver who killed a nun. Police say Sister Jackie Walsh, 59, was struck at around 8:30 p.m. yesterday on Rose Hill Road in Water Mill while out on a walk.Police say they found an unoccupied 2009 Volkswagen Touareg SUV with front end damage about a half-mile from the scene. They describe the suspected driver as a Hispanic male in his 20s or 30s, who's about 5 feet 7 inches tall, with short, spiked hair. Walsh was the former campus minister of Our Lady of Mercy Academy in Syosset. She was on the East End for a religious retreat with a number of other nuns from the Sisters of Mercy Order.People who knew Walsh say she was a key person in the parish over the past 10 years. Friends recalled her as a positive and outgoing person with a love for music."Because she's a Sister of Mercy, I think what Sister Jackie would want would be to extend her own mercy and forgiveness to whoever did this, to whoever took her life," Deacon Jim Murphy told News 12 Long Island.Meanwhile, police urge anyone with information to call the Southampton Detective Unit at 631-702-2230.