Taiikukan no Satsujin

After school, in an old high school gymnasium, a boy from the broadcasting club was found stabbed to death. The police immediately suspect the only person present in the locked gymnasium—the captain of the girls' table tennis club. Refusing to believe that their captain could be the culprit, a fellow club member seeks help from the school's top genius to uncover the truth. However, the genius turns out to be highly eccentric…

(Source: Natalie, translated)

Note: Manga adaptation of the first entry in Aosaki Yuugo's Urazome Tenma series.