Police have arrested three alleged extremists this week, as pressure mounts to act against those responsible, though none of the suspects have been publicly accused of direct involvement in the firebombing in the West Bank village of Duma.
One suspect, Mordechai Mayer, an 18-year-old settler, was placed yesterday in what is known as administrative detention, which allows him to be held indefinitely without charge.
He was accused in a defence ministry statement of involvement in "violent activities and terrorist attacks in recent times".
"The investigation into the murder in the village of Duma is the top priority of the police," a spokeswoman said in a statement today.
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"That is why it is necessary to use all the means at the police's disposal, including an appeal to the public," she added, calling on residents to report anything they knew.
Administrative detention dates from British-mandated Palestine, and Israel normally applies it against Palestinians, allowing them to be held without trial for renewable six-month periods.
Friday's firebombing also critically injured the boy's parents and four-year-old brother.
Just hours earlier, an ultra-Orthodox man was arrested for storming a Gay Pride march in Jerusalem and stabbing six people, mortally wounding a 16-year-old girl.
The suspect, Yishai Schlissel, had been released from prison only three weeks earlier after serving a 10-year sentence for a similar attack.
The two incidents have led to a wave of calls for a crackdown on Jewish extremists.