"After careful consideration of the facts of the case, a thorough review of the state investigation, and an extensive review of all applicable law, I have determined that no criminal charges should be filed against Lt. Mark Tiller at the state level," said Solicitor Chrissy Adams of the 10th Judicial Circuit.
Meanwhile, the U.S. Justice Department is continuing its civil rights investigation into the Seneca incident, Adams said.
Tiller welcomed the prosecutor's announcement, his attorney said.
"Lt. Tiller agrees with the outcome of the investigation. As stated from day one, Lt. Tiller acted in self-defense and the decision today supports this position," attorney John M. Mussetto said in a statement.
The Hammond family attorney, however, disagreed with the prosecutor's decision. They have been contending that police used excessive force.
"We're very disappointed in that the solicitor didn't bring any state law criminal charges," said attorney Eric Bland, who represents Hammond's parents, Paul and Angie.
While the family respects the prosecution's review of the case, "we vehemently disagree with her conclusion," Bland said.
"If you look at the (police dashcam) video, it's clear that he didn't follow any proper police procedure," Bland said, referring to Tiller.
Hammond's family has contended the teenager's civil rights were violated.
In August, Angie Hammond said she didn't feel Seneca authorities were "being honest about a lot of things."
A slow-motion video of the shooting, taken by a police dashboard camera, was released Tuesday by authorities.
The prosecutor detailed her reasons for not filing charges in a letter to the South Carolina Law Enforcement Division, which investigated the officer-involved shooting.
Hammond was shot by Tiller on July 26 in a parking lot of a Hardee's fast-food restaurant in Seneca.
The incident began when Hammond's date, Tori Morton, 24, mistakenly sent a text message offering to sell cocaine and marijuana to a phone number belonging to a South Carolina Highway Patrol trooper, Adams said in the letter, which was posted on CNN affiliate WYFF's website.
The trooper's cell number differed by only one digit from the intended recipient.
The trooper called the Seneca police narcotics unit, which then set up a meeting with "Tori" identified in the text message, Adams said in the letter.
Sgt. B.J. McClure parked and waited in the lot. Under a plan, he would radio the tags of a Honda Civic carrying "Tori" to marked units so they could perform a traffic stop on the highway, Adams said.
McClure didn't plan to complete the drug transaction, Adams said.
But the plan was abandoned after Hammond parked his car directly next to McClure, and then Hammond and Morton were about to exit their car and approach McClure, Adams said.
McClure called Tiller as backup, Adams said.
Tiller arrived in uniform in a marked vehicle with lights and sirens, and he pulled his car behind Hammond's parked car, Adams said.
Tiller exited his squad car and approached Hammond's car with his gun drawn, Adams said in the letter.
The unarmed teen didn't heed the officer's command to stop and show his hands.
Hammond began to drive off.
"Hammond then turns the car hard left toward Lt. Tiller, resulting in Lt. Tiller being face to face with Hammond at the driver's window," Adams said in the letter.
Tiller backpedaled to avoid being knocked down and pushed himself away from Hammond's car. His feet are about to go underneath Hammond's car, Adams said.
Tiller fired at Hammond.
"Two shots are fired in rapid succession," Adams said in the letter.
Different take on incident
Hammond family attorney Bland disagreed with Adams' conclusion.
"If you flee a traffic stop, it's a death sentence. We think it's wrong, and we think the solicitor got it wrong," Bland said.
"Zachary, no question, tried to leave. But it's clear he didn't turn to run over Lt. Tiller, but Tiller put himself in a position of danger," Bland said.
"Tiller just comes in hot," Bland said. "He put himself in harm's way so he could use deadly force."
Tiller, instead, could have put down his gun and called for backup and a roadblock, Bland said.
"Zachary wasn't fleeing to hurt someone. He was fleeing because someone came at him with a gun," Bland said.
Hammond's body tested positive for marijuana, cocaine and Levamisole, a cutting agent commonly used in cocaine, and packaged cocaine and was found in Hammond's shorts pocket, Adams said in the letter posted on WYFF's website.
"The evidence from this investigation corroborates and supports Lt. Tiller's belief that he was going to be run over. Therefore, the only conclusion that can be rendered is that deadly force was justified," Adams said in the letter.
Hammond "was actively resisting arrest and attempting to evade arrest by flight," the prosecutor wrote.
Hammond had an outstanding warrant for his arrest for failure to appear in court, and his text messages showed he had no intention of stopping for police and going to jail, the prosecutor said.
Police gathered 854 pages of Hammond's text messages between May 29 and July 26.
"Hammond talks about being in 'in full outlaw mode' and that he would 'go out shootin'. In fact, Hammond had the word 'Outlaw' tattooed on his left forearm the month prior to his death," the prosecutor wrote.
"Almost every text message deals with Hammond selling drugs to multiple individuals including marijuana, acid, cocaine and prescription pills," Adams wrote. "The text messages indicate that Hammond had been on a dangerous and destructive course for a significant period of his life."
"This has been a very difficult case," Adams concludes in the letter. "What happened during this encounter is a tragedy. No parent should ever have to bury their child."