They agreed to pay $40 for marijuana and were waiting outside a McDonald’s restroom at Verizon Center for the dealer inside to weigh the pot on a set of scales.

But only two in the group had money. A 17-year-old pitched in $30. A 20-year-old threw in $10. They told the indigent 15-year-old that “he couldn’t smoke with them,” according to a D.C. police criminal affidavit.

The youngest of the group told his friends that he would “bag” the dealer — street parlance for robbery, the affidavit says. In court documents filed Wednesday, D.C. police said that the 15-year-old burst into the restroom, took out a brown-handled rusty revolver and said, “You might as well give it up.”

According to the affidavit, the teenager then shot a 25-year-old man in the left side of the head — “without provocation” — as the victim squatted on the floor over the scales, 10 ounces of marijuana spilling to the floor. Police said the younger three left the restaurant without any drugs.

For the first time, these new details describe what led to the Aug. 12 shooting that occurred shortly before noon at the crowded restaurant in the arena, located in the 600 block of F Street NW, a street normally teeming with people headed to restaurants, theaters and other attractions.

[D.C. police arrest suspects in McDonald’s shooting]

Police arrested the 15-year-old on Aug. 13 and charged him as a juvenile with assault with intent to kill. But details of the case remained shrouded because paperwork and court proceedings involving juveniles are not public. Additional information became available after Tuesday, when police arrested the 17-year-old, also a juvenile, and 20-year-old Lafayette Booker of Northeast.

Booker was charged with assault with intent to rob. On Wednesday, a D.C. Superior Court judge ordered him detained until a preliminary hearing Friday. Booker’s attorney did not return calls seeking comment.

Police described the restaurant as packed at the time of the shooting and added that although patrons might not have heard the gunshot, the affidavit says the victim stumbled out of the restroom and collapsed in the middle of the floor near the front counter, bleeding “profusely from the ear.” A patron pressed his shirt over the wound.

The victim remains in critical condition at a hospital. In court documents, police described him as making a slow, painful recovery, at times appearing responsive and alert but unable to speak. At one point, because his jaw was wired shut, detectives used hand signals to elicit information about possible suspects.

Police quoted Booker telling them, “They shot him for nothing.”