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German authorities are hunting for a Tunisian man suspected in Monday's truck attack on a Christmas market in Berlin, which left 12 people dead and nearly 50 injured.

The 23-year-old suspect's documents were found inside the cab of the truck used to mow down civilians at the market.

He was identified as "Ahmed" or "Anis A.," among other suspected aliases, according to German police sources.

The suspect, who applied for asylum in Germany in April and received a temporary stay permit, reportedly has extensive links to militant Islam.

Retired Navy SEAL Rob O'Neill, the man who killed Usama bin Laden, joined Steve Doocy on "Fox & Friends" to discuss the latest in the manhunt and how we can more effectively combat terrorism.

Noting that the terrorist behind the Nice truck attack was also from Tunisia, O'Neill said this reinforces the need for more extensive vetting from "hot spots" of radicalism.

He criticized German Chancellor Angela Merkel's decision to accept hundreds of thousands of refugees from the Middle East and Africa.

O'Neill explained that Merkel made the same mistake that many on the far-left do, basing her decisions on emotion, as opposed to common sense and concern for the safety of German citizens.

He said that President-elect Donald Trump must learn from Merkel and other leaders' mistakes.

Watch more above.

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