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William Cummer, 42, had been missing for three days. (Saint John Police)

A potentially dangerous prisoner, who had been unlawfully at large for three days, was arrested in Saint John on Sunday night, according to the police.

The Saint John Police say William Cummer, 42, was taken into custody on Sunday night at a home on Peters Street in the Waterloo Village area.

The police had issued a warning on Friday that Cummer had been missing for three days and should not be approached.

Cummer was wanted on a Canada-wide arrest warrant.

Police say he has an extensive criminal background involving numerous violent offences.

It's not clear how he came to be at large.

Cummer is expected to appear in court on Monday morning.