Dana Seetahal died shortly after midnight on Sunday when people in two cars opened fire after cutting off her vehicle on a street in Trinidad's capital of Port-of-Spain.
There have been no arrests, but National Security Minister Gary Griffith said "we will not rest until those who have committed this most unspeakable act are brought to justice".
A government statement said Seetaha's slaying appeared to be a "well-orchestrated hit".
After the killing, officials said they would provide special security to a judge and several lawyers involved in the high-profile murder trial of wealthy businesswoman Vindra Naipul-Coolman. Seetahal was one of the prosecuting lawyers in the trial, which started on March 24.
Prime Minister Kamla Persad-Bissessar convened an emergency meeting of the national security council and described the killing as an "outrageous act of brutality".