Mr Blake was shot in the back seven times by Mr Sheskey after attempting to leave the scene of a domestic dispute. Officers claimed Mr Blake had a knife at the time, but Mr Blake's lawyers contend that the claim is untrue.
Mr Graveley also said Mr Blake would not be charged with any crimes.
He said an independent use of force expert, Noble Wray, was brought in to provide unbiased analysis of the shooting.
Mr Graveley said it was the DA's ethical obligation not to bring charges if it was clear that a case would not stand up in court.
He said that with the evidence available, the DA could not defeat Mr Shesky's claims of self-defense in court.
"The question to jury would be did officer Shesky reasonably believe that shooting at Jacob Blake be necessary to avoid being stabbed by him or to protect someone else from being harmed," he said.
Mr Graveley said that the burden of proof is on the DA to disprove the claims of self-defense, and that the perspective of self-defense has to be argued from the perspective of the officer, not from those witnessing the events.
"The jury would be instructed they can't use 2020 hindsight, they have to talk about what decision would be reasonable for an officer in the shoes of officer Shesky in that moment," he said.
Mr Graveley played a 911 call from domestic dispute in which Laquisha Booker, Mr Blake's fiance, says shes afraid he is going to steal the SUV and crash the vehicle.
He said the officers were sent to the scene and were told he had an arrest warrant for domestic violence offense and sexual assault.
Mr Graveley said Mr Blake had a pattern of domestic abuse, and said officers would have been thinking in those terms when they arrived at the scene.
He went on to say the officers were obligated to try to arrest Mr Blake because he had a felony arrest warrant for his arrest. He said that Mr Blake resisted arrest several times during the confrontation.
“Three attempts to tase Mr Blake were used to try to get him into compliance,” he said.
He then claimed that Mr Blake armed himself with a knife, saying it is “absolutely uncontroversial” that he had a knife, and that Mr Blake himself told investigators he was holding a knife.
He said Mr Blake, with knife in hand, twisted his body toward Mr Shesky, which prompted him to shoot. Mr Graveley pointed out that Mr Shesky immediately moved to provide medical assistance to Mr Blake following the shooting.
According to Mr Graveley, Mr Blake admitted that he had an argument with his fiance, that he took the keys to her rented SUV, that he had a knife, that he pulled the tasers out of himself, and that he had a knife. He also said Mr Blake claimed he was unaware that he had a warrant for his arrest.
However, texts from Mr Blake’s phone showed that he was aware of his warrant. Mr Graveley said that defense attorneys for the police would use that information, as well as details from a 2010 case in which Mr Blake allegedly drew a knife on officers and swiped at them, to establish that Mr Blake had motive to harm the officers.
Mr Blake's attorney, Ben Crump, said the decision was disappointing in the moments after the decision was made.
"We are immensely disappointed and feel this decision failed not only Jacob and his family but the community that protested and demanded justice," Mr Crump wrote on Twitter.
Mr Blake was shot seven times by Mr Sheskey while trying to get into an SUV rented by his fiance to drive away from the scene of a domestic dispute.
Mr Graveley said medical examiners reported that three shots were into Mr Blake’s left side, which he argued would be consistent with claims that he tried to turn and stab Mr Shesky. He said that the argument would have been made to support Mr Shesky’s claims of self defense if the case had gone to court.
Mr Wray, a former Wisconsin police captain, was brought onto the case as an independent use of force expert and said Mr Blake displayed “extreme resistance” to arrest. He said it was unusual that the tasers did not work on Mr Blake.
Mr Wray, addressing the number of shots, said officers in Wisconsin were trained to shoot “until the threat has stopped,” and that there would have been no way between the rapid shots to tell if Mr Blake had dropped the knife.
He ultimately determined the range of shots was acceptable considering the situation, and that the response was proportional, but acknowledged that the public may not see it that way.
Police claimed Mr Blake was reaching for a knife, but Mr Crump, claimed there was no knife in the car.
The Wisconsin Attorney General claimed that the state recovered a knife, which Mr Blake's lawyers claim was not in his possession at the time of the shooting.
Cellphone video captured the confrontation. Police attempted to use tasers on Mr Blake and to wrestle him to the ground, but were unsuccessful. Bystanders said they heard officers shout "drop the knife" but did not see any weapons. Other bystanders said that Mr Blake did not appear to be acting violently.
Mr Sheskey said he believed Mr Blake was attempting to kidnap the children in the SUV. The children were Mr Blake's.
Mr Wray say no officer would allow someone to leave with a child - even their own child - in a car under the circumstances of the encounter, claiming it was the "stuff Amber alerts were made of.”
Tanya McLean, executive director of the grassroots organization Leaders of Kenosha, told Wisconsin Public Radio that the community members she represents want to see Mr Sheskey brought to justice.
"Officer Sheskey fired seven shots into an unarmed man's back, on a block where our children walk to school and our families go to church," she said. "All of us — Black, white, brown, native and newcomer — deserve to be safe in our own neighborhoods, and that means holding police officers accountable when they brutalize us."
Mr Wray, who is Black, said the case was difficult and that he wished he could provide the Black community with an example of the justice system working for them, but that his ultimate obligation was “to truth” and that the criminal justice system is a “hard, harsh system” with a history of racism that he has struggled with for 30 years.
Mr Graveley said moving forward that every police officer in Kenosha should be equipped with a body camera.
The state activated the National Guard, and 500 troops were moved to Kenosha in anticipation of protests resulting from the decision.
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