DENVER, Colorado — Tom Sullivan, whose son Alex died in a mass shooting inside a Century 16 movie theater in Aurora, Colorado in 2012, unseated Republican incumbent Cole Wist to win the state House seat for District 37.

As of early Wednesday morning, Sullivan had 53 percent of the votes with 95 percent of results reported.

Sullivan, a veteran, is a proponent of gun control. He's visited the Colorado state Capitol more than 20 times to testify in favor of of various gun control measures.

Sullivan's son Alex was killed along with 11 others on his 27th birthday when a gunman opened fired in a movie theater during a showing of "The Dark Knight Rises" on July 20, 2012.

The murder of his son has been a motivation in Sullivan's political career.

ALL OF THE TEARS RIGHT NOW ACROSS THE COUNTRY: Tom Sullivan, whose beloved son Alex was shot and killed in an Aurora movie theater, is now a Colorado state representative. Thank you fellow Coloradans. Thank you. #coleg #copolitics https://t.co/1De3bh4owH — Shannon Watts (@shannonrwatts) November 7, 2018

In 2013, he worked with other families whose children had also been killed in shootings, such as Aurora, Newtown and Columbine. The efforts helped state Democrats push for tighter gun-control measures.

District 37 was previously considered a Republican stronghold and covers Aurora, Centennial and parts of Foxfield in Colorado.

Sullivan previously ran for state Senate in 2016 but lost to Republican Sen. Jack Tate.