Police say the two suspects are cousins.
The person with firsthand knowledge of DiNardo's confession said the men were killed after DiNardo felt cheated or threatened during three drug transactions.
Kratz allegedly shot Finocchiaro.
Police have charged Cosmo DiNardo, 20, with four homicide counts and 20 other crimes, including abuse of corpse, conspiracy and robbery. Both were being held in jail without bail.
The memorial ceremony is set for the Garden of Reflection 9/11 Memorial in Newtown Township, the hometown of one of the victims, Jimi Taro Patrick, 19.
The four killings took place in three separate incidents, each of which involved using marijuana to lure the men to Dinardo's property, according to a probable cause affidavit.
DiNardo, whose parents own the farm, remained in custody on $5 million cash bail, accused so far only of a gun possession charge and trying to sell one of the victims' cars.
The mystery of the four men's disappearances transfixed the Philadelphia area over the past week, taking a grisly turn when human remains were discovered in a 12½-foot-deep grave on a farm. Kratz was arrested later the same day, authorities said.
In exchange for this admission, Dinardo hopes to be able to avoid the death penalty, according to his lawyer.
While the news this week of the quadruple homicide in Bucks County has come out in spurts, Friday afternoon's release of the arrest affidavit reveals almost the entirety of the grisly events that led to the death of four young men.
Bucks County DA
"I can't predict the future, but that is what I believe", Weintraub said.
Here's what we know about the mysterious disappearances and the investigation that has consumed this suburban community and riveted the nation. "I'd like to think that he wanted to help us get these boys home". The suspect reportedly told investigators where on the Solebury Township property they could find Patrick after prosecutors agreed to take the death penalty off the table. "I talked to him just about every day", said neighbor Bill Hale.
It's not clear why Dinardo cooperated. Kratz spoke to investigators on Thursday night.
Patrick, 19, was shot and killed on July 5, and Dinardo allegedly used a backhoe to dig a 6-foot-deep hole and bury him, the affidavit states. He's since been charged alongside DiNardo for taking part in three of the killings. The charging documents state that DiNardo used a backhoe to pick up both men's bodies, put them in the same metal tank as Finocchiaro and poured gasoline into the metal tank and lit it.
He told prosecutors he agreed to sell Finocchiaro a quarter pound of weed for $700 on Friday. Another person, Sean Kratz was also charged. DiNardo, who was diagnosed with schizophrenia, buried Patrick in the hole and later gave authorities the specific location where his remains could be found.
They then placed him in a metal tank that Dinardo referred to as the pig roaster, according to the criminal complaint.
It was the discovery of Meo's auto on a DiNardo family property a half-mile from the farm that led to DiNardo's re-arrest. Sturgis then attempted to run away, prompting DiNardo to shoot him until he ran out of ammunition.
At this point, court documents say, Meo was screaming in pain and Dinardo climbed into a backhoe and ran over the injured Meo, killing him. He said he took Finocchiaro in his auto but kicked him out after declining to sell him drugs and then spent the rest of the night fishing.
"There was an attempt to burn the bodies, to deface them, to obliterate them, but I don't believe that that was successful", Weintraub said. They have a construction company and cement.