The Army Reserves soldier, who fatally stabbed a 20-year-old man on the steps of Manhattan's main post office Sunday, appears to have committed suicide Tuesday evening, according to unconfirmed reports.

The body, which is believed to be that of Sir'mone McCaulla, 28, was found inside his ex-girlfriend's Philadelphia apartment on Pine Street.

Philadelphia police contacted the NYPD, who have been searching for McCaulla since Sunday, and New York investigators rushed to the home.

Reports say the body was found slumped over in a water-filled tub with a plastic bag of his head. The body was also clutching a cable box in front of his chest, which suggests he electrocuted himself.

The NYPD has not confirmed the identity of the body, but sources close to Philadelphia police say authorities believe the body does belong to McCaulla.

Madina Jackson, McCaulla's cousin, told reporters police informed her family that he was dead.

The man believed to be McCaulla was transported to a local hospital in Philadelphia where he was pronounced dead at 6:27 p.m. Tuesday evening.

McCaulla was on active duty for the Army as a specialist stationed in Fort Totten in Queens. He previously served Kuwait, according to NYPD Commissioner Ray Kelly. McCaulla had previous run-ins with the law and was arrested three times for charges including burglary and robbery.

Three people called the NYPD's Crime Stoppers tip line after photos, taken by nearby a German tourist couple, were released to the public. One of the tipsters recognized McCaulla from their shared time in the military.

McCaulla stabbed and killed Christopher Guiterrez in broad daylight on the steps of the James A. Farley Post Office in midtown Manhattan. The murder was apparently triggered after words were exchanged when the two men accidentally bumped shoulders.

Guiterrez took off his jacket and readied himself for a fist fight when McCaulla advanced towards him while gripping a knife.

"As they got closer, the prepetrator lunges - four quick strokes or jabs - into the victim," said Kelly in a press conference.

Gutierrez collapsed in front of the post office and was pronounced dead at Bellevue Hospital on Sunday.

The murder scene is across the street from other busy landmarks -- Madison Square Garden and Penn Station.

Guiterrez worked as a stocker at a midtown grocery store and leaves behind a 1-year-old son. His wake is scheduled for Wednesday and Guiterrez's funeral will be held at the Ortiz Funeral Home on the Lower East Side, according to family members.