Demi Cuccia

MONROEVILLE — A tumultuous teenage relationship ended tragically when an 18-year-old man fatally stabbed his cheerleader girlfriend a day after her 16th birthday, then slashed his own throat, police said.

Demi Cuccia was killed late Wednesday while she was home alone. A neighbor said she had been ordered by her mother to stay away from John Mullarkey Jr.

Moments after neighbors heard screams, Mullarkey came out of the house and cut his throat, police and witnesses said. He was in critical condition Thursday.

The two-year relationship was well-known in the high school, where Cuccia was a cheerleader and Mullarkey had just graduated, with plans to attend community college. Friends referred to the relationship as "delicate" and "on and off."

Donna Walko, 48, who lives several doors away in the townhouse complex where Cuccia lived, described Mullarkey as possessive and jealous.

"I talked to Demi plenty of times. She was sitting in my living room. I begged her to get away from him," said Walko, whose two teenage daughters were fellow cheerleaders and friends of Cuccia.

Cuccia's mother had forbidden her from seeing him, said Walko.

Although the relationship was rocky, the attack shocked many who knew the pair. They said Mullarkey was funny and not violent, Cuccia friendly and popular.

"A lot of people didn't sleep last night because you don't think it would happen in Monroeville," said Kaitlin Nemec, 16, a friend of Cuccia.

But national statistics show it is not that rare for teenage relationships, fraught with high emotion, to turn violent.

Women ages 16 to 24 suffer the highest per capita rate of dating violence, according to a 2000 report by the U.S. Justice Department. One in three high school students has been or will be in an abusive relationship, and most teen dating violence takes place in the home of one of the partners, the report found.

Police Chief George Polnar said no charges were immediately filed because Mullarkey's prognosis was poor.

He said police were not aware of the two having a violent relationship.

"Generally, at that age, it doesn't graduate to this level," Polnar said.

On Thursday, neighbors at the secluded row of townhouses moved from house to house to talk about the killing, comforting one another and discussing the chain of events.

Fellow students set up a page on Facebook.com titled "R.I.P. Demi Cuccia." Within hours, friends and classmates had written their memories, thoughts and feelings.