The British politician stabbed and shot three times on a street in West Yorkshire had received hate mail from a man in the months leading up to her death, according to British media.
The Times reported that local police had planned to organise additional security for Labour MP Jo Cox after the harassment she was receiving intensified over the three-month period before she was killed.
The publication said Ms Cox had "thought little" of the abuse she was subject to until its "volume and frequency stepped up".
The man sending her threatening messages had apparently been warned over his actions. It is not yet known whether the hate mail's author is the same man who killed her.
Ms Cox's killer has been named as Tommy Mair, who lived nearby and has been described as a reclusive gardener by neighbours.
When police arrived, he was handcuffed and dragged to the side of the road, pinned down with his face pressed to the concrete.
However, the motives behind the brutal attack which left one of the Labour Party's most promising MPs bleeding in the street remain a mystery.