AS HE WAS laid to rest in West Philadelphia yesterday, Christian Massey - the 21-year-old gunned down in Overbrook last month for his headphones - wore the same mask of serenity that he carried through much of his short life.

Friends and relatives remembered Massey, a special-needs man who was mainstreamed into Marple Newtown High and played two years of varsity football there, as a trusting, pleasant young man with a passion for life.

In the days after the killing of the gregarious 6-foot-2, 300-pound "gentle giant," the story of his tragic death - of the thug who pumped two bullets into him over a $300 pair of Beats by Dr. Dre headphones - garnered his family a groundswell of support.

Late last night, a police source confirmed that Arkel Garcia, 19, was in police custody as Massey's suspected killer. Charges against Garcia and two other suspects in Massey's killing were pending last night, the source said.

At Massey's funeral at Hickman Temple AME Church on Baltimore Avenue near 50th Street, a collage of photos - most showing him beaming with his arm around someone - flanked his casket.

Scores of mourners reminisced about the times Massey made them laugh, the jovial way he carried himself, and how he found positives in negative situations.

"Christian didn't have that in him to get angry. He didn't let things like the bus not showing up bother him," Marple Newtown assistant principal and athletic director Dennis Reardon said, referring to times Massey's bus would fail to pick him up and Reardon or another faculty member would give him a ride home.

"I'll remember Christian as a kind person who overcame a lot of obstacles to be successful. He took full advantage of his opportunity to graduate high school . . . What's most important is that he never felt any different than anyone else. He was just one of the guys, and the guys treated him like he was one of them."

Marple Newtown is now trying to raise funds to present an annual scholarship in Massey's memory. After a Daily News story detailing Massey's family's financial struggles in the wake of his killing, Special Olympics provided a cemetery plot, while the Crime Victims Compensation Act defrayed expenses for his funeral.

In eulogizing Massey, Mike McGowan, his Special Olympics basketball coach for five years, recalled how Massey never let life challenge him despite the obstacles he faced.

"It was amazing how he approached each basketball game and how he approached life. He never let a challenge go by," McGowan told the gathering of about 400 people at the funeral. "I don't know how I'm ever going to be able to step on a basketball court again without thinking of him."

Cecile Matthews, head of the Life Skills Program at Marple Newtown, responsible for mainstreaming special-needs students, recalled Massey's kindness when he worked in a program that paired high-school seniors with preschool children to mentor.

"Chris' kindness to every person he met is something I'll remember him for," Matthews said. "Being around people made Chris happy. He made everyone around him a better person. He was always the rainbow at the end of the storm."

Donations for the memorial scholarship fund in Massey's memory can be sent to Marple Newtown High School, care of Dennis Reardon, 120 Media Line Road, Newtown Square, Pa., 19073.