Benanel Merah said police who surrounded his son's Toulouse apartment "could have used sleep-inducing gas and taken him like a baby" instead of shooting him dead, France 24 reported Wednesday.
Police said Mohamed Merah, 23, killed seven people over a 10-day span, including three French paratroopers of north African decent, and a rabbi, his two young children and another child outside a Jewish school in Toulouse. After a 2-day standoff at his apartment building, Merah was shot and killed Thursday in an operation in which three officers were injured.
"Why were they so hasty? Why did they kill him?" Benanel Merah said during his interview with France 24 Tuesday. "He could have been sentenced to many years in prison or even a life sentence. There is no death penalty in France."
The elder Merah earlier told reporters he would "hire the biggest named lawyers and work for the rest of my life to pay their costs -- I will sue France for having killed my son."
Abdelkader Merah, another son, is under investigation on suspicion of aiding and abetting in his brother's crimes.
On Tuesday, French leaders criticized Benanel Merah's threat to sue.
"[If] I was the father of a monster [like Merah] I would shut my mouth in shame," Foreign Minister Alain Juppe told Radio Classique.
Henri Guaino, chief adviser to President Nicolas Sarkozy, told France Culture radio that initiating legal proceedings would be "indecent," even though the father was "perfectly within his rights" to do so.
"A little bit of decency right now would do everyone a lot of good. To try to blame the state is the height of indecency," Guaino said. "This monster killed in cold blood. French society owes him absolutely nothing."