BERLIN — The German authorities unveiled a new memorial in Berlin on Tuesday, honoring the 12 people killed in the terrorist attack at a Christmas market last year, but their families and some survivors accused the government of failing to deport the attacker before he could strike and of a lack of empathy and support since the attack.

Before the ceremony, Chancellor Angela Merkel joined members of the acting government, President Frank-Walter Steinmeier and representatives from Berlin at a memorial service open only to survivors of the attack and the victims’ families. Michael Müller, the city’s mayor, dedicated the memorial in Breitscheid Square, where the attack took place.

It was a year to the day that the attacker, Anis Amri, drove a stolen truck into the crowded square, killing 12 people and injuring dozens of others. Mr. Amri, who died in a shootout with the Italian police days after the attack, had been under scrutiny by German security agencies for months before, but repeated opportunities to deport him were missed.