A man was killed in a New York City subway early Sunday morning, according to authorities. Police say that he was pushed onto the tracks by a currently unidentified assailant.

According to the New York Times, 61-year-old Wai Kuen Kwok and his wife were pushed in front of a southbound D train in The Bronx while they were on their way to breakfast in Manhattan’s Chinatown. Kwok was killed, while his wife survived without injury. She was taken to a hospital as a precaution.

Police have not yet identified Kwok’s murderer. He ran up the stairs, into the street, and boarded a bus immediately after the incident.

The mystery assailant didn’t steal anything from Kwok or his wife, and none of the witnesses said that they saw the two involved in an altercation of any kind. Authorities believe that the New York City subway murder was an act of random, meaningless violence. That the assailant merely saw the opportunity to murder the couple and took it.

Though most subway stations around the world use plastic guard rails to protect travelers from falling onto the tracks, New York City has thus far declined to invest in this safety precaution. City authorities say that the barriers would run each subway station about $1 million, citing budget woes and the relative rarity of subway-related deaths per year in their rationale.

“It is such a rare occurrence that no matter how tragic it is [subway deaths], it shouldn’t change our lifestyle,” said former mayor Michael Bloomberg in 2013.

According to The Atlantic, about 50 people die in New York City subways each year. Most are suicides.

Below is CCTV footage of the New York City subway murder suspect.