Police discovered the Bloomfield teen's body off Riverdale Road on the property of McIntosh Dairy farm a day after her boyfriend reported her missing on December 28.
The affidavit recounts what Lopez told authorities, not necessarily what detectives believe.
Two huge questions remain for authorities: Why did Bollinger have enough heroin in her system to kill her when she was shot? And did the suicidal thoughts that friends said Bollinger previously expressed play a role in her death?
After the killing, investigators initially focused on Shawn Shwartz, a man who Bollinger had at one point obtained a restraining order against, according to the affidavit.
He'd been posting repeatedly on Facebook about Bollinger's death, and in early January, those posts appeared to threaten self-harm, according to the Broomfield Enterprise. He was charged on Jan. 10 with assaulting police officers who were conducting a welfare check on him.
Shwartz told the Daily Camera that he's been questioned by police, but maintains he has done nothing wrong - and that Bollinger was his friend.
Lopez, the man accused of killing Bollinger, had not known her for very long, McIntosh said at the news conference.
Investigators said they had singled out Lopez after interviewing Bollinger's friends and sifting through her messages.
They asked him Thursday as he arrived for work at Domino's Pizza if he was willing to answer some questions, the Denver Channel reported.
According to the arrest affidavit, he said "he was pretty sure he knew what we were there for . . . he was sure it had to do with the girl he talked to on Craigslist."
He then told investigators how he had come in contact with Bollinger, according to the affidavit.
He said he stumbled across a strange ad combing through the "Women seeking Men" section on Craigslist, according to Denver NBC-affiliate WBGA, and then messaged Bollinger pretending to be a hit man. He agreed to meet and kill her after a long conversation via text. Authorities uncovered more than 100 text messages between the pair.
They discussed how she wanted to be killed, and how he would be paid afterward. As they drove around, he said in the affidavit, he tried to talk her out of it, but she was adamant. She'd even brought her own gun, he said.
He initially denied he was with her when she died, but investigators countered with evidence that showed his cellphone at the scene of the crime, the affidavit said.
Then he told them about Bollinger's final moment, according to court documents.
He said Bollinger "knelt down on the ground and that he knelt down along her left side and slightly in front of her." He then claimed they both said a prayer, he got up, closed his eyes and shot the teen.
Then, he told investigators, he fled with Bollinger's purse and the gun.
Investigators say Bollinger's body had a lethal amount of heroin in it when she was found, although the gunshot was the cause of death.
McIntosh was adamant at Friday's news conference that investigators may not have uncovered the true motive.
"Just because we have a suspect in custody, doesn't mean the investigation is over," McIntosh said.
