Centre County District Attorney Stacy Parks Miller made the announcement to reporters on Friday, saying 18 students were culpable.
On Friday, eight fraternity members, including the fraternity president, were charged with involuntary manslaughter, according to Philly.com. Ten additional members face other charges, including hazing, tampering with evidence and furnishing alcohol to minors.
An attorney for the chapter didn't immediately respond to messages seeking comment.
Those charged with involuntary manslaughter were Brendan Young of Malvern, president of the Beta Theta Pi chapter at Penn State, and fellow fraternity members Daniel Casey of Ronkonkoma, N.Y.; Jonah Neuman of Nashville, Tenn.; Nick Kubera of Downingtown; Michael Bonatucci of Woodstock, Ga.; Gary Dibileo of Scranton; Luke Visser of Encinitas, Calif.; and Joe Sala of Erie.
The Beta Theta Pi fraternity had a history of hazing and heavy drinking, and the grand jury investigation documented several other cases, including another incident where a student fell and suffered a head injury and help wasn't sought until the next day. "And when they finally did call for help they did not tell anyone that he had fallen", Miller said.
Piazza died at a hospital two days later, on February 4.
Miller said doctors estimate Piazza had a blood-alcohol content of almost 0.40 percent; the legal limit for drivers, for comparison, is 0.08 percent.
Frat members were accused of trying to cover up what happened.
At another point, one fraternity brother tackled another, landing on top of Piazza. "This didn't have to happen".
Timothy Piazza died after a fall at a fraternity pledge event at the Beta Theta Pi Fraternity House in February.
At a press conference, Penn State president Eric Barron called the details in the grand jury finding heart wrenching and incomprehensible.
Barron says it's "numbing" to see that a unsafe atmosphere could occur at a fraternity that prided itself on commitment to each other and the community.
Miller said video footage turned over to investigators provided evidence of what occurred and contradicted stories some witnesses had told. Prosecutors said Piazza consumed enormous amounts of alcohol as part of a hazing ritual and that members waited almost 12 hours after he first fell to call paramedics.
Piazza regains consciousness and is seen grabbing his abdomen, staggering and falling, prosecutors say surveillance video shows. A second attempt to stand later again caused him to fall face first. Four brothers carried his limp body back upstairs, where some poured liquid on him and one slapped him in the face, the jury said.
The fraternity, the grand jury said, "cultivated such a permissive atmosphere regarding excessive alcohol consumption, that Timothy Piazza's death was not simply an unfortunate accident, but was the direct result of encouraged reckless conduct that demonstrated a reckless disregard for human life, or a reckless indifference to the possible consequences of such conduct".
In an interview with "Good Morning America" that aired Sunday, Beta Theta Pi brother Kordel Davis says despite his repeated pleas to call 911, no one did. He later tried again, but was allegedly told that other members were biology and kinesiology majors, so his opinion meant less. He fell onto a stone floor at 5 a.m. "Also, Tim Piazza might actually be a problem", a fraternity brother wrote in a group text, the Times reported.