It is not clear if the figure in dark clothing is Holder, who police say is wanted in the homicide.
Los Angeles Police Commissioner Steve Soboroff read an email that was sent by Nipsey Hussle - whose given name is Ermias Asghedom - or a representative of Roc Nation to a large press corps.
Two other people were injured in the shooting incident but survived, according to a Los Angeles Police Department spokesman.
Moore told reporters that Holder and Hussle knew each other, but Moore did not disclose any details about the nature of the dispute.
"This has been a tough few days for Los Angeles", Los Angeles Mayor Eric Garcetti said, speaking of Hussle's advocacy for the community. "The absolute worst way to pay back Nipsey's loss.is with more violence".
Boeing, FAA say more time needed for fix of troubled 737 Max
One pilot, according to the Wall Street Journal , said to the other "pitch up, pitch up!" before their radio died. Chicago-based Boeing is under intense scrutiny after two crashes since October killed 346 people.
Eric Holder, the suspected killer of Nipsey Hussle, has been arrested and is in police custody.
The Los Angeles Times said several people were stabbed after a fight broke out at the vigil and two people were in a critical condition. One victim was hospitalized, and the other treated at the scene.
Nineteen people were transported to the hospital, majority with trample injuries, the Los Angeles Fire Department said.
"The community is the one that is helping us solve this case", Moore said.
Lauren London is opening up for the first time since the sudden death of her longtime partner and L.A. rap legend, Nipsey Hussle. Moore said he was not dismissing their claims, but police still have not confirmed that any gunfire occurred. "It will happen when Roc Nation and Nipsey's family come together".