Los Angeles police say two suspects have been arrested for the murder of 5-year-old Aaron Shannon, and are being held without bail. Leonard Hall Jr., 21, was taken into custody today (Friday) about at 2:10 a.m. at an apartment in the 200 block of West. 27th Str. Marcus Denson, 18, was arrested Thursday evening by Sheriff’s deputies in the 1100 block of East 83rd Street. Law enforcement officials say both suspects are active gang members.

Shannon was in his backyard in the 1000 block of East 84th Street at about 2 p.m. on Halloween–showing his uncle and grandfather his Spider-man trick-or-treating costume–when two suspected gang members opened fire from an alley behind the house, wounding him in the head.

He died the following day at a hospital.

Denson and Hall were each being held in lieu of $1 million bail, according to Los Angeles County Sheriff’s Department jail records. Denson was arrested Thursday night, and Hall was arrested this morning.

On Tuesday, a reward of up to $75,000 was offered for information leading to the suspected gang members who fatally shot the boy.

“On a day when little kids look forward to dressing up and going out and knocking door-to-door and going to parties to get candy and have some fun, this child was shot in the head by two people,” said Councilwoman Jan Perry, who proposed the reward.

“It is a horrible, heinous thing that these two people did and all we ask is that anybody who knows anything or saw anything or may have some information, to please call 77th Division (police detectives) and offer your information,” Perry said.

LAPD homicide Detective Eric Crosson of the LAPD’s 77th Street Station, said bullets grazed the grandfather’s arm and the uncle’s leg, but the boy was shot in the back of the head.

The shooting is linked to a gang rivalry between the Kitchen Crips and Swan Bloods, investigators said. The neighborhood where Aaron lived is an active gang area, but his family had no ties to gangs.

Fox11 reported two Crips members crossed Central Avenue on Sunday looking for Bloods to target when they opened fire on Aaron and his relatives.

“Every homicide angers me, but a 5-year-old on Halloween getting ready, that just tears at my heart,” LAPD Capt. Dennis Kato of the 77th Street Station told Fox11.

Of the gunmen, Perry said, “This is just wanton, horrid, homicidal people who have no regard for human life that they would shoot people in this manner.”