By Tony Hanson

PHILADELPHIA (CBS) — Did bullying lead a teenager to commit murder?

A Philadelphia homicide detective has testified the 15-year-old defendant confessed, admitting he killed another teen inside a Kensington home in October after weeks of taunting and threats.

Now, the teen has been held for trial.

Defendant Alexander Rodriguez told police he shot and killed 17-year-old Joel Gutierrez because he was mad.

“He said the motive was that he believed the victim was bullying him, saying that he is not tough, that he’s going to steal his girlfriend from him,” recounts Philadelphia prosecutor Carlos Vega.  “And just kept on every day, when he’d see him he’d say, ‘You’re nothing, wanna fight?’  And the defendant did not want to have a fistfight.  So he decided to arm himself with a shotgun, put on a mask, and shot him in the head with a shotgun.”

Rodriguez told police he dumped the gun, the mask, and other clothing in the river.

Vega, the prosecutor, says the defendant’s avowed motive will be central to the case:

“At this point in time we have nobody to verify other than the defendant that he was bullied.  And even if he were bullied, the deceased in this case only called him names and asked if he wanted to fight.  The defendant declined, and he never even struck him.”