Both Adams and Wilson said they knew the suspects "from the neighborhood."
Sheriff's officials did not immediately return a phone call or emails seeking clarification on how the shooting began.
In September, Stewart pleaded guilty to making a terroristic threat — a misdemeanor — after being part of a group that in December assaulted and then threatened to kill a student at Cypress Woods High School. Stewart was sentenced to five days in jail. Last month, Stewart was charged with check forgery. Young was arrested earlier this year for evading arrest but the charge was later dropped.
Monday's arrests came on the same day that school officials said security will be boosted and grief counselors provided for students at a school where one of the slain teens was enrolled.
Katy school district spokesman Steve Stanford said Richardson was a student at Morton Ranch High School.
Stanford said some students at the school were among the more than 100 who attended the party in nearby Cypress. He said school district police will increase patrols so that officers are more visible this week.
"It's not because of any threat," Stanford said. "It's more to reassure students."