How to get your handcuffs off without a a key

in the film "no country for old men" the beginging the bad guy kills a cop using his handcuffs to brutally strangle the cop, but how did he get them out? sure he mightve reached for the officer's keys but how can his hands do that if they cant move? plus his handcuffs are in the front, not the backside, therefore making it much easier to strangle a person