Image captionPerez is pregnant with the couple’s second child
Ms Perez, who is pregnant, is facing charges of second degree manslaughter. She faces her first court appearance on Wednesday.
County Attorney James Brue described the book as a hardcover encyclopaedia, and said the weapon used was a .50-calibre Desert Eagle handgun.
Police have seized two cameras, which are said to have recorded Monday’s incident.
The single gunshot was fired from about one foot (30cm) away as neighbours gathered to watch outside their Minnesota home.
She told deputies that the stunt had been Ruiz’s idea, and that he had to convince her to do it.
Earlier that day she tweeted about her reservations.
“Everyone was crying. I was standing behind that tree over there. And that was it. I just couldn’t take it anymore so I had to go back home,” neighbour Wayne Cameron told WDAY-TV.
The couple had started a YouTube channel in March, aiming to show the “the real life of a young couple who happen to be teen parents”.
Their most recently uploaded video, on the day that Ruiz died, was titled: “Doing scary stunts at the fair”.
Last week Ms Perez told her viewers that it was a “blessing” to have her husband home for the forthcoming birth of their son, who is due in September.