Footage captures the moment a man bought a knife he used to kill his estranged wife - before he lay in wait outside her house to stab her to death.Cold blooded Satpreet Singh Gandhi, 37, was then captured on security cameras running off from Harleen Kaur Satpreet Gandhi's flat after killing her.Police said Gandhi killed Harleen, 32, because she ended their abusive relationship six months earlier, police said.SWNS