BETHLEHEM, Pa. (AP) _ A man was arrested in the murders of two teen-age girls at a popular campus lookout five months ago in a case that stunned this quiet community, police said today.

Officers would say only that the person arrested was a male, saying a news conference would be held later today. But one victim's mother said police told her the girls knew the suspect.

Mary Orlando, 15, and her best friend Jennifer Grider, 17, were shot to death June 29 as they settled on the hill above Lehigh University to have a picnic.

KYW-AM Newsradio in Philadelphia said Christopher Bissey, 18, of Salisbury Township was arrested around midnight and arraigned on murder charges.

Police last month said they had no suspects and were stumped as to who killed the girls. The radio station quoted Bethlehem police Capt. Herbert Goldfeder as saying the break came from a telephone tip about five days ago.

``My first reaction was I felt sick,'' said Joan Grider, mother of the elder victim, 17-year-old Jennifer. ``Everything came back and we had to live through it again. I feel relief but I don't have the answers yet. I still don't know why. I feel relief also because we've all been living in fear, looking behind our backs.''

Grider said police told her the suspect and the girls were acquainted, although she and her husband, Carl, do not know Bissey.