1 ARRESTED IN SHOOTING OF COUPLE : WITNESSES SAID KILLER WALKED AWAY LAUGHING.

Byline: Matthew Yi Associated Press 

Police arrested a 70-year-old man who they said gunned down a pair of young lovers in a crowded park and walked away chuckling.

Margrito Franco was booked on charges of murdering 15-year-old Sylvia Menendez and 18-year-old Carlos Hernandez.

The killings Sunday had appeared to be random - a man approached the couple as they lounged under a tree, spoke briefly, then fired in front of dozens of witnesses - and residents of the neighborhood that prided itself on winning its battle against crime were horrified.

On Friday, police said Franco apparently knew Menendez, but authorities would not elaborate on how he knew her or comment on a motive for the shootings.

A pistol found in Franco's home eight blocks from the park matched the bullets in the shooting, police said.

Hernandez and Menendez had just arrived at Precita Park from church when they were slain.

According to witnesses, a man collecting cans in the park approached the couple and talked to them briefly. He then fired at Hernandez. When Menendez reached over to protect her boyfriend, she, too, was shot.

Police Chief Fred Lau said investigators were flooded with calls from witnesses and put out a sketch of the killer. By Tuesday, Franco had become the prime suspect.

Residents for years had rallied around Precita Park, a onetime gang hangout known as ``Needle Park'' because of the drug users it attracted. Investigators said there was nothing to indicate gangs or drugs were involved in the killings.

The victims were described as extraordinarily devoted to each other. Both were members of the Seventh-day Adventist Church, where they sang in the choir. Menendez, friends said, was a bright ninth-grader. Hernandez recently had graduated high school and planned to become a pastor.