The three-member International Crimes Tribunal headed by Justice Md Shahinur Islam announced the verdict on Tuesday.
The convicts faced two cases of crimes against humanity, including wartime killings, rape, abduction, torture and arson.
Of the convicts, Akmal Ali Talukder, 79, was present in court during the verdict. The three others -- Abdun Noor alias Lal Miah, 66, Anis Miah, 80, and Abdul Mosabbir, 80, -- were on the run.
The tribunal kept the verdict pending after both the prosecution and the defence completed their closing arguments on Mar 27.
After the prosecution pressed charges against the four on May 31, 2016, the tribunal began the trial proceedings on May 7, 2017 against them.
The convicted were charged with killing 59 people, raping six and looting and arson attacks on 81 households, according to investigators.
The tribunal issued arrest warrants against the four on Nov 26, 2015 and police arrested Talukder from Pachgaon, Rajnagar on the same day.
Talukder, a retired senior vice-principal of a Qawmi madrasa in Moulvibazar town, was then sent to jail by the tribunal.
The investigation committee finalised the case report on Mar 23, 2016. The court began hearing the testimonies of witnesses on Jul 4.
This is the 33rd verdict since the ICT began the trial of suspects in 2010 for their roles in crimes against humanity during the 1971 Liberation War.