In what legal experts said was the first murder conviction won with help of a MetroCard, Christopher Stewart, 36, was found guilty yesterday after his alibi was demolished because Transit Authority computer records showed he used his card on mass transit.

Stewart said he was at the St. George ferry terminal on Staten Island on his way to Manhattan when his ex-girlfriend Angelique Williams, 29, was stabbed to death outside the Todt Hill Houses on March 8, 2001.

But Stewart's TA identification card, which doubled as a MetroCard, was used to board a southbound S54 bus about an hour before the 5:30 p.m. slaying. The bus passes Stewart's home in the Livingston neighborhood and the Todt Hill Houses.

MetroCard records also showed that Stewart's card was used to board a northbound S54 bus about 15 minutes after the murder.

The prosecution was boosted by the testimony of a 12-year-old boy, playing nearby, who identified Stewart.

Staten Island District Attorney William Murphy praised the team of detectives, including Nelson Ferrone, who thought of checking the TA's MetroCard database for clues.

"They virtually pinpointed the defendant's presence at the scene of the homicide at the time of the crime," Murphy said.

Stewart is the father of Williams' young daughter and had been charged previously with assaulting Williams. An order of protection had been issued against him.