Media rights groups have said Sri Lanka remains a dangerous place for journalists despite the end of a decades-long war between the military and Tamil separatist rebels in 2009.
Sri Lanka lifted a state of emergency in 2011, but media activists say journalists have been forced to self-censor their work due to fear of attacks.
But it said two military deserters were among those involved in the crime.
Five men held the editor at knifepoint and searched her Colombo home in a pre-dawn raid Saturday after saying they wanted to steal jewellery and cash, but police burst in and shot dead one of the intruders.
The island's main press freedom organisation, the Free Media Movement, said it suspected the robbery was linked to the work of Sunday Leader associate editor Mandana Ismail Abeywickrema.
However, the army and the police insisted it was an attempted robbery.
"It is deplorable that some parties (are) trying to implicate the army in this criminal act carried out by a gang of robbers