Two security guards were stabbed, one of them fatally, at a Macy’s store in center city Philadelphia on Monday by a man who tried to steal hats from the store, authorities said.

The man entered the store around 10:45 a.m. and attempted to steal several hats before being stopped by security and turned away, Philadelphia Police Department Interim Commissioner John M. Stanford, Jr. said at a news conference. on Monday.

The man returned to the store about 15 minutes later armed with a knife, and he “immediately headed straight for a security guard, then turned his attention away for a second,” Commissioner Stanford said.

A suspect fled the store on a subway train shortly after 11 a.m. He was found a short time later at the Somerset station northeast of the store, where he was arrested, the Southeastern Pennsylvania Transportation Authority said in a statement.

The victim has been identified as a 30-year-old shopkeeper. He was stabbed once in the neck and taken to a hospital, where he died, the Philadelphia Police Department said in a statement. Another victim, a 23-year-old security guard, was stabbed in the face and left arm and is in stable condition, police said.

“This started as a retail theft, apparently upgraded to a robbery, and then ultimately led to a murder,” Commissioner Stanford said. “It’s a sad situation.”

Defendants and suspects have not been publicly identified.

The transit authority said in a statement Monday that a third person was also injured in the attack, but the Philadelphia Police Department later said only two people were injured.

And it was not immediately clear what led to the stabbing. Commissioner Stanford said Monday that he did not want to speculate on the man’s motive, saying it “certainly appears” that the man attacked security guards in retaliation for taking back store items he tried to steal.

A Macy’s store is located on Market Street across from Philadelphia’s City Hall. Commissioner Stanford said Center City has “experienced a high level of retail theft” this year, adding that the store has had more than 250 reports of shoplifting.

“We are heartbroken by today’s incident,” Macy’s said in a statement on Monday.

The store was closed Monday as police investigated, Macy’s said.