A Joliet man was a roommate of the woman he’s charged with killing and the woman was apparently holding her 4-year-old son in her arms when they were repeatedly shot by him, prosecutors said.

New details in the first-degree murder case against Joseph Darnell Johnson, 29, were revealed in a petition filed on Monday by Will County Assistant State’s Attorney Tricia McKenna.

Johnson is charged with the Jan. 25 first-degree murder of Joselynn Diaz-Garcia, 36, and her 4-year-old son, Gianni Reyes, in the 700 block of Garnsey Avenue in Joliet.

Diaz-Garcia had “several injuries consistent with being beaten about her head and face,” according to McKenna’s petition.

Diaz-Garcia suffered five gunshot wounds while Reyes suffered four gunshot wounds, court records show.

Diaz-Garcia’s surviving 8-year-old son, who is nonverbal, was found by officers inside the residence asleep, she said.

McKenna’s petition argues Johnson is too dangerous to receive pretrial release in the case.

“The facts of this case, set forth below, show that the defendant killed not only a woman he had only known for a short period of time who allowed him in her home, but an innocent preschooler who appeared to have been in his mother’s arms at the time that both were repeatedly shot by him,” McKenna’s petition said.

A motive has not yet been uncovered by detectives with the Joliet Police Department.

A Will County judge is supposed to consider whether to keep Johnson in jail on Feb. 27.

Police interviews with Diaz-Garcia’s friends and family established she recently moved to the 700 block of Garnsey Avenue with her two children, McKenna said.

“Approximately two weeks before her death, she met [Johnson] through her friend’s boyfriend. [Johnson] moved in with her to assist her with paying with rent,” McKenna said.

Diaz-Garcia’s phone was broken a week before the shooting, which meant her only means of contacting people was through Johnson’s phone or her son’s tablet, McKenna said.

When officers responded other the shooting, they found Johnson lying with his face in the snow, shirtless and wearing “basketball-style” shorts with socks and no shoes, McKenna said.

“While officers were attempting to gather his name or any information regarding this event, he yelled, ‘[Expletive] you dead!’ toward the direction of the victims,” McKenna said.

A short pistol version of an AK-47 firearm was found with blood on it in the area, McKenna said.

“Numerous individuals reported seeing a person, shirtless and shoeless, holding the firearm, firing the firearm and heading toward the location where the defendant was then immediately located by police,” McKenna said.

On Jan. 27, officers tried speaking with Johnson while he was hospitalized at Loyola Medical Center in Maywood for a gunshot wound to the ankle that police believe is self-inflicted, according to police and prosecutors.

But Johnson asked for a lawyer once he was read his Miranda rights, McKenna said.

At one point later on, Johnson made a spontaneous statement to the effect of, “This was not supposed to happen,” McKenna said.