Police said they believe there were at least three shooters: a 15-year-old, an acquaintance who died at the scene and "at least one other unknown suspect."
Davy and Natalie Lloyd "were attacked by gangs this evening and were both killed," Natalie Lloyd's father, Missouri state Rep. Ben Baker, said in a Facebook post.
Another group of Americans was evacuated from Haiti on a US-chartered helicopter flight on Wednesday.
The sentencing comes two years after a shootout erupted during a planned robbery. Authorities said the series of events were connected to the outlaw motorcycle gang, Bandidos.
The US military said on Sunday it conducted an operation to airlift non-essential personnel from the US embassy and to bolster the security of its mission in the capital.
Investigators believe the 20-year-old shooting suspect was targeting people from a rival gang, but it is unclear if the victims were involved in any illegal activity.