This is the horrific moment an off-duty Spanish cop choked a suspected phone thief to death in front of passersby as they pleaded with him to 'let him breathe'.

The unnamed 58-year-old policeman was out for dinner with a friend on Tuesday in the Spanish town of Torrejon de Ardoz in northeastern Madrid when a man allegedly stole his phone and ran off.

The alleged thief was chased by the cop, who slammed him to the ground and held him in a neck restraint.

A disturbing video shows the police officer lying on the ground as he holds the man in a deadly chokehold.

'Call the police', the cop calls out to onlookers as his victim lies motionlessly on the pavement.