The cause of death for Colin Kroll, the co-founder and chief executive of HQ Trivia, has been determined to be a drug overdose, according to the final medical examiner’s report. The exact cause was listed as “acute intoxication due to the combined effects of fentanyl, fluoroisobutyryl fentanyl, heroin, and cocaine.” Kroll, 34, was found dead in his Lower Manhattan apartment in December. The technology developer co-founded popular apps Vine and HQ Trivia, after a tumultuous stint at Twitter, which ultimately bought Vine. HQ Trivia livestreams 15-minute trivia shows typically twice a day to tens of thousands of users. The app became a viral sensation last year, but has recently seen a drop off-in users.