HARRIS COUNTY, Texas -

Two brothers have been charged in connection to a deadly birthday party shooting at a Cypress-area home.

Randy Stewart, 18, who was already charged with aggravated assault with a deadly weapon in the shootings, has now been charged with tampering with evidence. His brother, Marvin Stewart, 20, is charged with concealing a gun that investigators say was apparently was used in the shootings.

Two teens, Arielle Shepherd and Qu'eric Richardson, were killed in the November shooting.  Nearly 20 other people were injured.  The suspects opened fire during a house party that had been advertised as a birthday celebration on Twitter and other social media.

According to the Harris County Sheriff's Office, the gun in the tampering case has not been found despite an extensive search.

The shootings remain under investigation.  There is a possibility that others will be charged with assaulting or killing some of the partygoers.