A man suspected of abruptly pulling a gun and killing a stranger on a New York City subway train has been arrested. But police say they don't yet know what motivated the apparently unprovoked attack. Andrew Abdullah was taken into custody on Tuesday, hours after authorities posted his name and photo on social media and implored the public to help find him. The 25-year-old is expected to face a murder charge in the death of 48-year-old Daniel Enriquez. Enriquez was shot to death while heading to brunch Sunday morning.