Vigils are not just spontaneous demonstrations of grief. They are carefully choreographed. Today, candlelight vigils are investigative tools for the American police.
1) Another opportunity for detectives to talk to suspects and witnesses.
2) Take pictures of the crowd and ID everyone there.
3) Opporunity to re-focus media attention
4) Get a family appeal to catch the suspect
5) Publicize the reward money
It’s theater. Even if the victim’s family doesn’t want to hold a vigil, the police will encourage it to help clear the crime.
Here’s a great example. Ice-cold case, a homicide from 2010. This “vigil” is not about grief; it’s about pinging the public for more information. Notice how the particpants are all holding up reward posters.