"We're extremely gratified by the jury's verdict," Washington County State's Attorney Charles Strong said after the trial concluded. Strong's office has filed court papers stating it will seek life imprisonment without the possibility of parole for Blankumsee.
Sentencing will be set after a pre-sentence investigation of Blankumsee's criminal history.
During his closing argument, Deputy State's Attorney Joseph Michael told the jury that when a homicide occurs during the commission of a felony - such as armed robbery - those responsible for the robbery also are responsible for first-degree murder.
"There's no free pass for poor marksmanship," Michael said.
He said that Blankumsee, who he admitted did not fire the .22-caliber bullet that killed Dennis, could have hit any of the other youths in the courtyard that morning with the .380-caliber gun he was seen holding by witnesses escaping the gunfire.
Attorneys for both sides stipulated Friday that Tyshawn Jones was found with the .22-caliber gun in his possession, which was linked to the bullet found in Dennis' chest. Jones' murder trial is scheduled for Jan. 4, according to court records.
Michael said Blankumsee's role in robbing Andrew Snyder, who was 13 years old at the time of the murder, of $8 and a pack of cigarettes was directly related to his role in firing bullets that morning at the group of Dennis' friends and relatives.
"He was the backup muscle at the robbery itself and the trigger puller in the hail of fire for the robbery escape," he said.
But Assistant Public Defender Brian Hutchison, co-counsel for Blankumsee, told a different version to jurors in his closing argument.
Hutchison pointed suspicion at Isreal Martinez, aka Fleet, who witnesses identified as being with Blankumsee at the 958C Security Road apartment party at Washington Gardens Apartments.
Hutchison said Martinez was from Waynesboro, Pa., and familiar to most of the partygoers, had a previous altercation with Dennis' brother and had been found with gunshot residue on his hands, which he said means Martinez "very well could have shot a gun that night."
Hutchison tried to cast doubt that Blankumsee played an active role in the robbery, saying that "at best" he was present when it occurred.
Martinez has not been charged in connection with the robbery or murder, Hutchison said.
Michael, in his rebuttal, attacked Hutchison's assertion that Blankumsee's role was minimal.
He called Martinez "a domino" who "will fall" when and if police get enough evidence to pursue charges against him.
"Just because Mr. Martinez is guilty, doesn't mean he's not," Michael said, pointing at Blankumsee.
Hutchison objected to a part of Michael's rebuttal concerning Martinez.
Circuit Judge Donald E. Beachley agreed with Hutchison.
"This is about the state versus Blankumsee," Beachley said.
"Exactly!" Michael said in an excited burst and walked briskly in front of the jury.
"This is about the state versus Blankumsee and not about the state versus Martinez," he said.
After the state and defense finished their closing arguments, a male juror who was seen sleeping was excused and replaced with a female alternate who had sat through the trial along with the original jurors.
The final jury that deliberated the verdict included five women and seven men. There was one black man on the jury.
There were about 25 family members and friends of Jonathan Dennis inside the courtroom Friday, who were present as the verdict was being read. Two women said they were attending on behalf of Blankumsee, and police and court officials filled the courtroom.
As each count was read, there were few sounds from the audience. Friends whispered a quiet "yes" after some of the "guilty" counts. There were some teary eyes.
Blankumsee whispered to Hutchison. He glanced at the audience. His face sometimes broadened into smiles, and other times closed to a blank stare as he flipped through pages on the table in front of him.
As the clerk checked the verdicts on the 28 counts with the jury, Blankumsee slumped onto the table, placing his head on his outstretched arm, continuing to watch the jury.