The viral video that showed three officers shooting an unarmed Mexican man last week in Pasco, Washington has been labeled as insufficient evidence in the investigation.

Fusion reports police said the video of the officers killing undocumented immigrant Antonio Zambrano-Montes cannot be used because they do not know who filmed the video or the device on which it was recorded.

"It's not enough for us to take [it] from YouTube," said Ken Lattin, a spokesperson for the Kennewick Police Department. "It has to be preserved forensically in order to be admitted as evidence."

Police could use footage from the dashcam present during the incident. Lattin said they could also use the microphones the three officers were wearing to determine if they addressed the victim in Spanish or not.

The officers involved in the shooting have been put on administrative leave while Lattin urges the person who killed Zambrano-Montes to step forward.

About 16 officers who are not from the Pasco Department are assisting with investigating the case while the crime lab places the case as top priority.

Lattin said police also need more evidence about Zambrano-Montes because they could not figure out what he was doing prior to the incident.

"It's curious that when you ask them about the past of some of the officers, they say that information is not pertinent to the investigation," said Felix Vargas, chair of Consejo Latino, a local organization of Latino-owned businesses. But somehow what Zambrano was doing weeks before this incident is vital information. We fully expect charges to be brought [against the officers] and for justice to be served."

Pasco police said officers shot the victim only after the Taser had no effect on him as he threw rocks at the officers, NBC News reports.

Nearly 40 witnesses of the shooting have stepped forward, and most of them were already interviewed.