1) the thieves were running / ran away when they were hearing / heard the police sirens. 2)the police were catching / caught the burglar as he escaped / was escaping from the back door. 3)the old woman was screaming / screamed when she was seeing / saw a stranger in her house.

1) The thieves ran away when they heard the police sirens.
2) The police caught the burglar as he was escaping from the back door.
3) The old woman screamed when she saw a stranger in her house.