A stabbing over the weekend in a South Philadelphia Starbucks that left a man critically injured has left investigators with a mystery, even after they charged a man with the attack.

Michael Singley, 52, of the 2000 block of Juniper Street, has been charged with attempted murder, but detectives are still unclear what instigated the assault, said Lt. Frank Vanore of the Public Affairs Unit.

The victim "was just sitting there waiting for his order and was very unclear why the complainant stabbed him," Vanore said this morning, adding that due to the victim's condition, investigators had a limited interview with him.

It's possible that that attack was unprovoked, Vanore said. Police initially were told there may have been an argument.

"It's clear the complainant was a very violent individual," Vanore said.

Singley is accused of repeatedly stabbing and slashing at a 29-year-old customer who was waiting for his order about 5:45 p.m. Saturday at the coffee shop at 2201 S. Broad St., between Jackson and Wolf Streets.

The victim, whom police did not identify, was stabbed multiple times in the body and at least once in the face. He remained in critical, but stable condition, at the Hospital of the University of Pennsylvania today, Vanore said.

In addition to attempted murder, Singley has been charged with aggravated assault, simple assault, possession of an instrument of a crime, and recklessly endangering another person.

Officers arrested Singley about 8 a.m. Sunday at the same Starbucks after witnesses called police and reported they recognized him as the assailant.