A 19-year-old Indianapolis man has been charged with killing three people over four days in attacks a prosecutor said he justified by citing the horror movie "The Purge," which is about one day a year when murder is legal.

A Marion County judge entered a not guilty plea for Johnathan Cruz and ordered him held without bond during an initial hearing Thursday on three murder counts and other charges for the attacks starting May 12.

Angela Barger, who told reporters after the hearing she was Cruz's girlfriend, said she was with him at least one day during that time and didn't believe he committed the crimes.

"They're making him out to be some type of crazy, violent person and he's not," she said. "Yeah, he had issues, but he wasn't that violent."

Detectives said a witness told them that Cruz confessed he had been "purging" by shooting and robbing people, according to court documents filed Wednesday. Police said this referred to the 2013 movie starring Ethan Hawke, in which during one night a year, all crime is legal. Detectives found a text message dated May 2 from Cruz saying "I Purge every night now."

Deputy Prosecutor Denise Robinson said authorities have cellphone video of at least part of one suspected attack.

"I can't get into his mind, but he certainly used the movie as at least his excuse or justification when he was recording himself committing these acts," she said.

Court documents say Cruz fatally shot Billy Boyd and Jay Higginbotham on May 12 and Jose Ruiz on May 15 during attacks on the city's east and north sides. He is also charged with the armed robbery of a man on May 14.

Barger and Ricki Cline, the mother of Cruz's 3-month-old daughter, said the people blaming Cruz for the killings are trying to protect themselves and that connections to "The Purge" have been blown out of proportion.

"It's irrelevant and it's pointless," Cline said.

The 2013 film focuses on what is called "The Purge," a nationwide catharsis, which runs for 12 hours once a year, during which violent crime including murder is encouraged as a patriotic duty. In the film, set in the year 2022, income inequality has reached such a level that the rich barricade themselves in their homes while the poor are vulnerable to the killing, which is promoted by government to cull the population. A sequel came out in 2014, and the series' third film is scheduled for release this summer.

Cruz was already jailed since his May 16 arrest on felony charges from a restaurant confrontation with a teenage girl two days earlier.

His public defender, Kendal Gulbrandsen, didn't immediately return telephone messages seeking comment.

In another incident that some people on social media linked to the movie, a high school student's hoax tweeted in August, 2014, about an impending "Louisville Purge," in which the Kentucky city would be overtaken by crime. The hoax kicked off a social media storm and prompted schools and other organizations to cancel events. No such purge took place.

Police declined to take action against the student, but Louisville Metro Police Department Sgt. Phil Russell said they took seriously any threat "that encourages and incites violence against our community."