Thunder of Gunfire, Splintering of Glass : Violence: Man recounts horror of best friend being shot in the back as they huddled for safety in the front seat of car. Gunman still at large.

Dan Sapinoso wanted to give his son a big party for his 20th birthday this December. Instead, Sapinoso and his wife, Josephine, struggled to get on with their life Sunday as they prepared to bury the polite, easygoing young man.

“My only son--he’s my only son. Everything is meaningless now,” Sapinoso said. “This will be like a tattoo on my heart.”

Robert Sapinoso was slain in a hail of gunfire Wednesday night as he and his closest friend followed a van whose occupants, they believed, were responsible for vandalism in the area.

“We were just trying to get a plate number, trying to do the right thing,” the friend, who asked that his name not be used for fear of reprisal, said Sunday.

Throughout the weekend, more than 100 of Robert Sapinoso’s friends and relatives gathered around a simple gray casket at Forest Lawn in Cypress and remembered the young man as generous, bashful and innocent.

“He’s a Good Samaritan guy. He just wants to help anybody who needs help,” his father said. “That’s the reason he got killed.”

As police continued searching for two suspects who drove off in the van, the 20-year-old friend on Sunday recalled the harrowing experience that claimed his friend, a computer whiz with a 3.8 grade-point average as an engineering student at UC Irvine.

They were tinkering on their cars about 6:45 p.m. Wednesday when they spotted a passing silver Toyota van that matched the description of one used by vandals in the area the previous weekend. They hopped into Sapinoso’s Honda CRX to follow the van.

With Sapinoso at the wheel, his friend said, they managed to get all but one digit from the license plate of the van, which pulled over two blocks away. But on their way home, as the pair stopped at a traffic light, a passenger emerged from the van and strode toward them, he said.

“The light was red. I told Robert, ‘Run it, Robert!’ By that time, the guy was coming up to the car,” according to the friend. “I thought he was going to kick the car. Then he pulled a gun from behind his back and started shooting.”

The friend, a college student in Orange County, huddled near the floor of the tiny car amid a thunder of gunfire and splintering glass. Sapinoso doubled over too, but was blocked by the steering wheel. When the shooting ended moments later, the friend was uninjured. He said he called to his buddy.

“I go, ‘Robert, are you OK?’ I looked at his face and his chest and he looked OK. Then . . . his eyes rolled back in his head,” the youth recalled.

When he noticed the wounds in Sapinoso’s back, the friend jumped from the car and screamed for help, but “there was no one out there or anything,” he said, deciding it would be quicker to race Sapinoso to a hospital a mile away. He wrestled Sapinoso from the driver’s seat and, with the shot-up driver’s door flapping, sped to Vencor Hospital- Orange County.

When they arrived, the youth’s cries for help drew a nurse who began cardiopulmonary resuscitation. “I was just praying, ‘Hold on Robert. Hold on. I thought, ‘Oh God, this isn’t happening,’ ” the friend said.

But at 7:16 p.m., Sapinoso was pronounced dead.

Police described the suspect as Asian, age 17 to 21. The gunman was bucktoothed and acne-scarred, according to the friend, who said, “if I saw him again, I’d know it.”

That knowledge scares him. He said he now fears that the gunman might try to hunt him or his family down--especially since he gave police a detailed description of the assailant. Police refused to release the composite.

“We’re scared because we don’t have any protection,” he said. “We’re really scared.”