The suspected shooter at Arapahoe High School may have been a student seeking revenge over a conflict with a teacher, Arapahoe County Sheriff Grayson Robinson said.
Sheriff Robinson said the identity of the gunman will not be released "until everything is confirmed".
More top news
After a relatively mild and quiet night, an episode of rain for many of us tomorrow.
The 34-year-old from Coulsdon in Surrey died during the private party in Headley in the early hours of Monday, Surrey Police said.
The Home Office made the arrests at various restaurants across London on July 4.