Eyewitness News has obtained surveillance video showing the shooting:
The gunman shot 55-year-old Imam Maulama Akonjee and 64-year-old Thara Uddin as they left afternoon prayers at a mosque in Ozone Park.
The suspect was described by witnesses as a man with a medium complexion, last seen wearing a dark shirt and blue shorts. Police released a sketch early Sunday of a dark-haired, bearded man wearing glasses.
Authorities say the shooter approached them from behind as they left the Al-Furqan Jame Masjid mosque in Queens shortly before 2 p.m. Both men were shot in the head.
Police say they haven't determined a motive. But members of the Bangladeshi Muslim community served by the mosque worry it could be a hate crime.
"There's nothing in the preliminary investigation to indicate that they were targeted because of their faith," said Deputy Inspector Henry Sautner of the New York Police Department.
Both men were wearing traditional religious attire and Akonjee was carrying about $1,000 in cash but the money was not taken.
Hundreds gathered gathered at a rally Saturday night to demand justice.
Police say there was no argument before the shooting - the man just approached and fired.
Services for Imam Maulama Akonjee will be held Monday at Bergen Funeral Home on Grant Avenue in Brooklyn. A memorial service will be held at 2 p.m.
(The Associated Press contributed to this report.)