NEW YORK (CBSNewYork) — An investigation is underway after an innocent woman was stabbed to death by a stranger just steps from her home on Staten Island Monday afternoon.

It’s a crime so gruesome the whole neighborhood is left reeling, wondering what would possess someone to attack someone so viciously.

Police initially responded to a report of an assault near the corner of Bement Avenue and Bement Court in Randall Manor just after 2 p.m.

Upon arrival, officers discovered the 63-year-old woman with at least 15 stab wounds to her face and torso along with 56-year-old Mark Long, a good Samaritan who was slashed in the arm in an attempt to save her.

Medics transported the woman, identified as Geetha Howie of Staten Island, to Richmond University Medical Center where she was pronounced dead.

Long was treated at the scene. He told CBS2’s Jessica Layton he heard the initial commotion and was slashed while trying to intervene.

“As I got closer I realized it was a man stabbing a woman,” Long said. “I moved in, I yelled at him to stop, I shouted out to one of the neighbors to call 911 and we just faced each other. I just tried to talk to him, keep his attention off the woman, and just basically tried to hold him there until the police got there.”

Sources tell CBS2 the 27-year-old suspect was cradling Howie’s body when police arrived at the scene. He was taken into custody without incident, according to police.

Howie’s family say she had just left the bank when she encountered the alleged killer. One relative believes it was a robbery-gone-wrong.

“She loved me, she loved her family,” son-in-law Daniel Fazzina said. “We have a three-year-old daughter who she absolutely loves. It was her granddaughter. They were just inseparable. It’s just a senseless tragedy.”

Fazzina tells CBS2 the entire family was in town and about to head to Sri Lanka for Howie’s nephew’s wedding. Instead, they’ll be planning a funeral for the beloved grandmother.

The investigation is active and ongoing as authorities work to determine a motive for the deadly stabbing.