Jashore had the previous highest temperature of the season at 42.6C
Chattogram District and Sessions Judge Md Ismail Hossain handed down the verdict on Monday afternoon.
Awami League chief Sheikh Hasina, now prime minister, was travelling to the rally site when police opened fire on her motorcade.
Twenty-four died in the unprovoked assault on Jan 24, 1988, during the regime of the late military dictator HM Ershad.
The attack was seen by Awami League leaders as an “attempt to assassinate” Hasina.