Also on Wednesday, a car bomb exploded in eastern Baghdad, killing at least 11 people and wounding another 58.
The unusually high 24-hour tally was recorded despite a month-old security crackdown in the Iraqi capital by US and Iraqi troops.
The source said most bodies were bound and shot in the head and many bore signs of torture - trademarks of sectarian death squads and kidnap gangs plaguing the capital.
The UN estimated two months ago that about 100 people a day were being killed in Iraq in fighting between the country's Shia and Sunni Muslim communities.
Sectarian killings in the capital have created waves of refugees, fleeing homes in neighbourhoods where they feel in a minority and hardening a divide along the Tigris river between mainly Sunni west Baghdad and the mainly Shia east.
Wednesday's deadly explosion in eastern Baghdad took place in a large square used mostly as a car park near the main headquarters of Baghdad's traffic police department. At least two of the dead were traffic police officers.
In a separate attack, three mortars were fired at al-Rashaad police station in Baghdad's eastern Jadida neighbourhood. The attack killed one policeman and wounded two others.
Another three mortars were fired at central Baghdad's Muthanna airport which left four civilians wounded.
The US military has announced that two American soldiers were killed in Iraq in separate attacks in the last two days.
One soldier was killed on Tuesday when his vehicle was struck by a roadside bomb south of Baghdad.
A second died on Monday of wounds received due to "enemy action" while operating in the western Anbar province.