The four-year starter earned All-Big Sky recognition in each season: honorable mention in 2012 and 2013, second-team in 2014, and first-team in 2015.

Between the Senior Bowl and the combine, it was reported he met with multiple teams, including the Cincinnati Bengals, Dallas Cowboys, San Diego Chargers, New York Jets, Detroit Lions, and the Indianapolis Colts' head coach Chuck Pagano.

[4] Over twenty scouts and representatives from NFL teams showed up to evaluate Killebrew and ten other prospects at SUU's Pro Day.

[6] After he had appeared in the senior bowl, the Lions safeties coach, Alan Williams, and other representatives from the organization had a meeting with Killebrew and told him that they were not interested in him, he wasn't a right fit for the team, and that they did not want him at all.

[8] He began his rookie season as the Lions' third strong safety on the depth chart behind veterans Tavon Wilson and Rafael Bush.

Four days later, he made four tackles on third down, while only appearing on nine of the Lions' defensive snaps during their 16–13 victory over the Minnesota Vikings on Thanksgiving.

[11][12] On September 10, 2017, in the Lions' season opening 35–23 victory over the Arizona Cardinals, Killebrew had a 35-yard interception return for a touchdown, which came off of quarterback Carson Palmer, in the fourth quarter.

[16] He recorded 12 total tackles (10 solo, two assisted) After the 2020 season, the Lions opted to not resign Killebrew, making him a free agent.